add security level negotiation between call creds and channel.

include/grpc/grpc_security.h

@@ -132,7 +132,8 @@ GRPCAPI void grpc_channel_credentials_release(grpc_channel_credentials* creds);
 
 /** Creates default credentials to connect to a google gRPC service.
    WARNING: Do NOT use this credentials to connect to a non-google service as
-   this could result in an oauth2 token leak. */
+   this could result in an oauth2 token leak. The security level of the
+   resulting connection is GRPC_PRIVACY_AND_INTEGRITY. */
 GRPCAPI grpc_channel_credentials* grpc_google_default_credentials_create(void);
 
 /** Callback for getting the SSL roots override from the application.
@@ -208,6 +209,7 @@ typedef struct {
 /** Deprecated in favor of grpc_ssl_server_credentials_create_ex. It will be
    removed after all of its call sites are migrated to
    grpc_ssl_server_credentials_create_ex. Creates an SSL credentials object.
+   The security level of the resulting connection is GRPC_PRIVACY_AND_INTEGRITY.
    - pem_root_certs is the NULL-terminated string containing the PEM encoding
      of the server root certificates. If this parameter is NULL, the
      implementation will first try to dereference the file pointed by the
@@ -239,6 +241,7 @@ GRPCAPI grpc_channel_credentials* grpc_ssl_credentials_create(
     const verify_peer_options* verify_options, void* reserved);
 
 /* Creates an SSL credentials object.
+   The security level of the resulting connection is GRPC_PRIVACY_AND_INTEGRITY.
    - pem_root_certs is the NULL-terminated string containing the PEM encoding
      of the server root certificates. If this parameter is NULL, the
      implementation will first try to dereference the file pointed by the
@@ -281,7 +284,8 @@ typedef struct grpc_call_credentials grpc_call_credentials;
    The creator of the credentials object is responsible for its release. */
 GRPCAPI void grpc_call_credentials_release(grpc_call_credentials* creds);
 
-/** Creates a composite channel credentials object. */
+/** Creates a composite channel credentials object. The security level of
+ * resulting connection is determined by channel_creds. */
 GRPCAPI grpc_channel_credentials* grpc_composite_channel_credentials_create(
     grpc_channel_credentials* channel_creds, grpc_call_credentials* call_creds,
     void* reserved);
@@ -431,9 +435,11 @@ typedef struct {
   const char* type;
 } grpc_metadata_credentials_plugin;
 
-/** Creates a credentials object from a plugin. */
+/** Creates a credentials object from a plugin with a specified minimum security
+ * level. */
 GRPCAPI grpc_call_credentials* grpc_metadata_credentials_create_from_plugin(
-    grpc_metadata_credentials_plugin plugin, void* reserved);
+    grpc_metadata_credentials_plugin plugin,
+    grpc_security_level min_security_level, void* reserved);
 
 /** --- Secure channel creation. --- */
 
@@ -653,8 +659,9 @@ GRPCAPI void grpc_alts_credentials_options_destroy(
     grpc_alts_credentials_options* options);
 
 /**
- * This method creates an ALTS channel credential object. It is used for
- * experimental purpose for now and subject to change.
+ * This method creates an ALTS channel credential object. The security
+ * level of the resulting connection is GRPC_PRIVACY_AND_INTEGRITY.
+ * It is used for experimental purpose for now and subject to change.
  *
  * - options: grpc ALTS credentials options instance for client.
  *
@@ -677,8 +684,10 @@ GRPCAPI grpc_server_credentials* grpc_alts_server_credentials_create(
 /** --- Local channel/server credentials --- **/
 
 /**
- * This method creates a local channel credential object. It is used for
- * experimental purpose for now and subject to change.
+ * This method creates a local channel credential object. The security level
+ * of the resulting connection is GRPC_PRIVACY_AND_INTEGRITY for UDS and
+ * GRPC_SECURITY_NONE for LOCAL_TCP. It is used for experimental purpose
+ * for now and subject to change.
  *
  * - type: local connection type
  *
@@ -940,7 +949,8 @@ grpc_tls_server_authorization_check_config_create(
 
 /**
  * This method creates a TLS channel credential object.
- * It takes ownership of the options parameter.
+ * It takes ownership of the options parameter. The security level
+ * of the resulting connection is GRPC_PRIVACY_AND_INTEGRITY.
  *
  * - options: grpc TLS credentials options instance.
  *

include/grpc/grpc_security_constants.h

@@ -30,6 +30,7 @@ extern "C" {
 #define GRPC_X509_SAN_PROPERTY_NAME "x509_subject_alternative_name"
 #define GRPC_X509_PEM_CERT_PROPERTY_NAME "x509_pem_cert"
 #define GRPC_SSL_SESSION_REUSED_PROPERTY "ssl_session_reused"
+#define GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME "security_level"
 
 /** Environment variable that points to the default SSL roots file. This file
    must be a PEM encoded file with all the roots such as the one that can be
@@ -105,7 +106,9 @@ typedef enum {
   GRPC_SSL_REQUEST_AND_REQUIRE_CLIENT_CERTIFICATE_AND_VERIFY
 } grpc_ssl_client_certificate_request_type;
 
-/* Security levels of grpc transport security */
+/* Security levels of grpc transport security. It represents an inherent
+ * property of a backend connection and is determined by a channel credential
+ * used to create the connection. */
 typedef enum {
   GRPC_SECURITY_MIN,
   GRPC_SECURITY_NONE = GRPC_SECURITY_MIN,

include/grpcpp/security/credentials_impl.h

@@ -321,6 +321,10 @@ grpc::Status StsCredentialsOptionsFromEnv(StsCredentialsOptions* options);
 std::shared_ptr<CallCredentials> StsCredentials(
     const StsCredentialsOptions& options);
 
+std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
+    std::unique_ptr<MetadataCredentialsPlugin> plugin,
+    grpc_security_level min_security_level);
+
 /// Options used to build AltsCredentials.
 struct AltsCredentialsOptions {
   /// service accounts of target endpoint that will be acceptable

src/core/lib/security/credentials/composite/composite_credentials.cc

@@ -151,6 +151,13 @@ grpc_composite_call_credentials::grpc_composite_call_credentials(
   inner_.reserve(size);
   push_to_inner(std::move(creds1), creds1_is_composite);
   push_to_inner(std::move(creds2), creds2_is_composite);
+  min_security_level_ = GRPC_SECURITY_NONE;
+  for (size_t i = 0; i < inner_.size(); ++i) {
+    if (static_cast<int>(min_security_level_) <
+        static_cast<int>(inner_[i]->min_security_level())) {
+      min_security_level_ = inner_[i]->min_security_level();
+    }
+  }
 }
 
 static grpc_core::RefCountedPtr<grpc_call_credentials>

src/core/lib/security/credentials/composite/composite_credentials.h

@@ -86,12 +86,16 @@ class grpc_composite_call_credentials : public grpc_call_credentials {
   void cancel_get_request_metadata(grpc_credentials_mdelem_array* md_array,
                                    grpc_error* error) override;
 
+  grpc_security_level min_security_level() const override {
+    return min_security_level_;
+  }
+
   const CallCredentialsList& inner() const { return inner_; }
 
  private:
   void push_to_inner(grpc_core::RefCountedPtr<grpc_call_credentials> creds,
                      bool is_composite);
-
+  grpc_security_level min_security_level_;
   CallCredentialsList inner_;
 };
 

src/core/lib/security/credentials/credentials.h

@@ -225,7 +225,11 @@ void grpc_credentials_mdelem_array_destroy(grpc_credentials_mdelem_array* list);
 struct grpc_call_credentials
     : public grpc_core::RefCounted<grpc_call_credentials> {
  public:
-  explicit grpc_call_credentials(const char* type) : type_(type) {}
+  explicit grpc_call_credentials(
+      const char* type,
+      grpc_security_level min_security_level = GRPC_PRIVACY_AND_INTEGRITY)
+      : type_(type), min_security_level_(min_security_level) {}
+
   virtual ~grpc_call_credentials() = default;
 
   // Returns true if completed synchronously, in which case \a error will
@@ -244,10 +248,15 @@ struct grpc_call_credentials
   virtual void cancel_get_request_metadata(
       grpc_credentials_mdelem_array* md_array, grpc_error* error) = 0;
 
+  virtual grpc_security_level min_security_level() const {
+    return min_security_level_;
+  }
+
   const char* type() const { return type_; }
 
  private:
   const char* type_;
+  const grpc_security_level min_security_level_;
 };
 
 /* Metadata-only credentials with the specified key and value where

src/core/lib/security/credentials/fake/fake_credentials.h

@@ -59,7 +59,8 @@ class grpc_md_only_test_credentials : public grpc_call_credentials {
  public:
   grpc_md_only_test_credentials(const char* md_key, const char* md_value,
                                 bool is_async)
-      : grpc_call_credentials(GRPC_CALL_CREDENTIALS_TYPE_OAUTH2),
+      : grpc_call_credentials(GRPC_CALL_CREDENTIALS_TYPE_OAUTH2,
+                              GRPC_SECURITY_NONE),
         md_(grpc_mdelem_from_slices(grpc_slice_from_copied_string(md_key),
                                     grpc_slice_from_copied_string(md_value))),
         is_async_(is_async) {}

src/core/lib/security/credentials/plugin/plugin_credentials.cc

@@ -240,15 +240,17 @@ void grpc_plugin_credentials::cancel_get_request_metadata(
 }
 
 grpc_plugin_credentials::grpc_plugin_credentials(
-    grpc_metadata_credentials_plugin plugin)
-    : grpc_call_credentials(plugin.type), plugin_(plugin) {
+    grpc_metadata_credentials_plugin plugin,
+    grpc_security_level min_security_level)
+    : grpc_call_credentials(plugin.type, min_security_level), plugin_(plugin) {
   gpr_mu_init(&mu_);
 }
 
 grpc_call_credentials* grpc_metadata_credentials_create_from_plugin(
-    grpc_metadata_credentials_plugin plugin, void* reserved) {
+    grpc_metadata_credentials_plugin plugin,
+    grpc_security_level min_security_level, void* reserved) {
   GRPC_API_TRACE("grpc_metadata_credentials_create_from_plugin(reserved=%p)", 1,
                  (reserved));
   GPR_ASSERT(reserved == nullptr);
-  return new grpc_plugin_credentials(plugin);
+  return new grpc_plugin_credentials(plugin, min_security_level);
 }

src/core/lib/security/credentials/plugin/plugin_credentials.h

@@ -39,7 +39,8 @@ struct grpc_plugin_credentials final : public grpc_call_credentials {
     struct pending_request* next;
   };
 
-  explicit grpc_plugin_credentials(grpc_metadata_credentials_plugin plugin);
+  explicit grpc_plugin_credentials(grpc_metadata_credentials_plugin plugin,
+                                   grpc_security_level min_security_level);
   ~grpc_plugin_credentials() override;
 
   bool get_request_metadata(grpc_polling_entity* pollent,

src/core/lib/security/security_connector/alts/alts_security_connector.cc

@@ -178,6 +178,13 @@ grpc_alts_auth_context_from_tsi_peer(const tsi_peer* peer) {
     gpr_log(GPR_ERROR, "Invalid or missing certificate type property.");
     return nullptr;
   }
+  /* Check if security level exists. */
+  const tsi_peer_property* security_level_prop =
+      tsi_peer_get_property_by_name(peer, TSI_SECURITY_LEVEL_PEER_PROPERTY);
+  if (security_level_prop == nullptr) {
+    gpr_log(GPR_ERROR, "Missing security level property.");
+    return nullptr;
+  }
   /* Validate RPC protocol versions. */
   const tsi_peer_property* rpc_versions_prop =
       tsi_peer_get_property_by_name(peer, TSI_ALTS_RPC_VERSIONS);
@@ -232,6 +239,12 @@ grpc_alts_auth_context_from_tsi_peer(const tsi_peer* peer) {
                                      tsi_prop->value.data,
                                      tsi_prop->value.length);
     }
+    /* Add security level to auth context. */
+    if (strcmp(tsi_prop->name, TSI_SECURITY_LEVEL_PEER_PROPERTY) == 0) {
+      grpc_auth_context_add_property(
+          ctx.get(), GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME,
+          tsi_prop->value.data, tsi_prop->value.length);
+    }
   }
   if (!grpc_auth_context_peer_is_authenticated(ctx.get())) {
     gpr_log(GPR_ERROR, "Invalid unauthenticated peer.");

src/core/lib/security/security_connector/fake/fake_security_connector.cc

@@ -219,9 +219,9 @@ static void fake_check_peer(
   const char* prop_name;
   grpc_error* error = GRPC_ERROR_NONE;
   *auth_context = nullptr;
-  if (peer.property_count != 1) {
+  if (peer.property_count != 2) {
     error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
-        "Fake peers should only have 1 property.");
+        "Fake peers should only have 2 properties.");
     goto end;
   }
   prop_name = peer.properties[0].name;
@@ -240,10 +240,30 @@ static void fake_check_peer(
         "Invalid value for cert type property.");
     goto end;
   }
+  prop_name = peer.properties[1].name;
+  if (prop_name == nullptr ||
+      strcmp(prop_name, TSI_SECURITY_LEVEL_PEER_PROPERTY) != 0) {
+    char* msg;
+    gpr_asprintf(&msg, "Unexpected property in fake peer: %s.",
+                 prop_name == nullptr ? "<EMPTY>" : prop_name);
+    error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(msg);
+    gpr_free(msg);
+    goto end;
+  }
+  if (strncmp(peer.properties[1].value.data, TSI_FAKE_SECURITY_LEVEL,
+              peer.properties[1].value.length) != 0) {
+    error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+        "Invalid value for security level property.");
+    goto end;
+  }
+
   *auth_context = grpc_core::MakeRefCounted<grpc_auth_context>(nullptr);
   grpc_auth_context_add_cstring_property(
       auth_context->get(), GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME,
       GRPC_FAKE_TRANSPORT_SECURITY_TYPE);
+  grpc_auth_context_add_cstring_property(
+      auth_context->get(), GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME,
+      TSI_FAKE_SECURITY_LEVEL);
 end:
   grpc_core::ExecCtx::Run(DEBUG_LOCATION, on_peer_checked, error);
   tsi_peer_destruct(&peer);

src/core/lib/security/security_connector/local/local_security_connector.cc

@@ -46,7 +46,8 @@
 
 namespace {
 
-grpc_core::RefCountedPtr<grpc_auth_context> local_auth_context_create() {
+grpc_core::RefCountedPtr<grpc_auth_context> local_auth_context_create(
+    const tsi_peer* peer) {
   /* Create auth context. */
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_core::MakeRefCounted<grpc_auth_context>(nullptr);
@@ -55,10 +56,17 @@ grpc_core::RefCountedPtr<grpc_auth_context> local_auth_context_create() {
       GRPC_LOCAL_TRANSPORT_SECURITY_TYPE);
   GPR_ASSERT(grpc_auth_context_set_peer_identity_property_name(
                  ctx.get(), GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME) == 1);
+  GPR_ASSERT(peer->property_count == 1);
+  const tsi_peer_property* prop = &peer->properties[0];
+  GPR_ASSERT(prop != nullptr);
+  GPR_ASSERT(strcmp(prop->name, TSI_SECURITY_LEVEL_PEER_PROPERTY) == 0);
+  grpc_auth_context_add_property(ctx.get(),
+                                 GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME,
+                                 prop->value.data, prop->value.length);
   return ctx;
 }
 
-void local_check_peer(grpc_security_connector* /*sc*/, tsi_peer /*peer*/,
+void local_check_peer(grpc_security_connector* sc, tsi_peer peer,
                       grpc_endpoint* ep,
                       grpc_core::RefCountedPtr<grpc_auth_context>* auth_context,
                       grpc_closure* on_peer_checked,
@@ -103,12 +111,30 @@ void local_check_peer(grpc_security_connector* /*sc*/, tsi_peer /*peer*/,
     grpc_core::ExecCtx::Run(DEBUG_LOCATION, on_peer_checked, error);
     return;
   }
+  // Add TSI_SECURITY_LEVEL_PEER_PROPERTY type peer property.
+  size_t new_property_count = peer.property_count + 1;
+  tsi_peer_property* new_properties = static_cast<tsi_peer_property*>(
+      gpr_zalloc(sizeof(*new_properties) * new_property_count));
+  for (size_t i = 0; i < peer.property_count; i++) {
+    new_properties[i] = peer.properties[i];
+  }
+  if (peer.properties != nullptr) gpr_free(peer.properties);
+  peer.properties = new_properties;
+  // TODO(yihuazhang): Set security level of local TCP to TSI_SECURITY_NONE.
+  const char* security_level =
+      tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY);
+  tsi_result result = tsi_construct_string_peer_property_from_cstring(
+      TSI_SECURITY_LEVEL_PEER_PROPERTY, security_level,
+      &peer.properties[peer.property_count]);
+  if (result != TSI_OK) return;
+  peer.property_count++;
   /* Create an auth context which is necessary to pass the santiy check in
    * {client, server}_auth_filter that verifies if the peer's auth context is
    * obtained during handshakes. The auth context is only checked for its
    * existence and not actually used.
    */
-  *auth_context = local_auth_context_create();
+  *auth_context = local_auth_context_create(&peer);
+  tsi_peer_destruct(&peer);
   error = *auth_context != nullptr ? GRPC_ERROR_NONE
                                    : GRPC_ERROR_CREATE_FROM_STATIC_STRING(
                                          "Could not create local auth context");

src/core/lib/security/security_connector/ssl_utils.cc

@@ -84,6 +84,30 @@ const char* grpc_get_ssl_cipher_suites(void) {
   return cipher_suites;
 }
 
+grpc_security_level grpc_tsi_security_level_string_to_enum(
+    const char* security_level) {
+  if (strcmp(security_level, "TSI_INTEGRITY_ONLY") == 0) {
+    return GRPC_INTEGRITY_ONLY;
+  } else if (strcmp(security_level, "TSI_PRIVACY_AND_INTEGRITY") == 0) {
+    return GRPC_PRIVACY_AND_INTEGRITY;
+  }
+  return GRPC_SECURITY_NONE;
+}
+
+const char* grpc_security_level_to_string(grpc_security_level security_level) {
+  if (security_level == GRPC_PRIVACY_AND_INTEGRITY) {
+    return "GRPC_PRIVACY_AND_INTEGRITY";
+  } else if (security_level == GRPC_INTEGRITY_ONLY) {
+    return "GRPC_INTEGRITY_ONLY";
+  }
+  return "GRPC_SECURITY_NONE";
+}
+
+bool grpc_check_security_level(grpc_security_level channel_level,
+                               grpc_security_level call_cred_level) {
+  return static_cast<int>(channel_level) >= static_cast<int>(call_cred_level);
+}
+
 tsi_client_certificate_request_type
 grpc_get_tsi_client_certificate_request_type(
     grpc_ssl_client_certificate_request_type grpc_request_type) {
@@ -229,6 +253,10 @@ grpc_core::RefCountedPtr<grpc_auth_context> grpc_ssl_peer_to_auth_context(
       grpc_auth_context_add_property(ctx.get(),
                                      GRPC_SSL_SESSION_REUSED_PROPERTY,
                                      prop->value.data, prop->value.length);
+    } else if (strcmp(prop->name, TSI_SECURITY_LEVEL_PEER_PROPERTY) == 0) {
+      grpc_auth_context_add_property(
+          ctx.get(), GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME,
+          prop->value.data, prop->value.length);
     }
   }
   if (peer_identity_property_name != nullptr) {
@@ -272,6 +300,10 @@ tsi_peer grpc_shallow_peer_from_ssl_auth_context(
       } else if (strcmp(prop->name, GRPC_X509_PEM_CERT_PROPERTY_NAME) == 0) {
         add_shallow_auth_property_to_peer(&peer, prop,
                                           TSI_X509_PEM_CERT_PROPERTY);
+      } else if (strcmp(prop->name,
+                        GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME) == 0) {
+        add_shallow_auth_property_to_peer(&peer, prop,
+                                          TSI_SECURITY_LEVEL_PEER_PROPERTY);
       }
     }
   }

src/core/lib/security/security_connector/ssl_utils.h

@@ -68,6 +68,17 @@ tsi_client_certificate_request_type
 grpc_get_tsi_client_certificate_request_type(
     grpc_ssl_client_certificate_request_type grpc_request_type);
 
+/* Map tsi_security_level string to grpc_security_level enum. */
+grpc_security_level grpc_tsi_security_level_string_to_enum(
+    const char* security_level);
+
+/* Map grpc_security_level enum to a string. */
+const char* grpc_security_level_to_string(grpc_security_level security_level);
+
+/* Check security level of channel and call credential.*/
+bool grpc_check_security_level(grpc_security_level channel_level,
+                               grpc_security_level call_cred_level);
+
 /* Return an array of strings containing alpn protocols. */
 const char** grpc_fill_alpn_protocol_strings(size_t* num_alpn_protocols);
 

src/core/lib/security/transport/client_auth_filter.cc

@@ -266,6 +266,39 @@ static void send_security_metadata(grpc_call_element* elem,
         call_creds_has_md ? ctx->creds->Ref() : channel_call_creds->Ref();
   }
 
+  /* Check security level of call credential and channel, and do not send
+   * metadata if the check fails. */
+  grpc_auth_property_iterator it = grpc_auth_context_find_properties_by_name(
+      chand->auth_context.get(), GRPC_TRANSPORT_SECURITY_LEVEL_PROPERTY_NAME);
+  const grpc_auth_property* prop = grpc_auth_property_iterator_next(&it);
+  if (prop == nullptr) {
+    grpc_transport_stream_op_batch_finish_with_failure(
+        batch,
+        grpc_error_set_int(
+            GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+                "Established channel does not have an auth property "
+                "representing a security level."),
+            GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAUTHENTICATED),
+        calld->call_combiner);
+    return;
+  }
+  grpc_security_level call_cred_security_level =
+      calld->creds->min_security_level();
+  int is_security_level_ok = grpc_check_security_level(
+      grpc_tsi_security_level_string_to_enum(prop->value),
+      call_cred_security_level);
+  if (!is_security_level_ok) {
+    grpc_transport_stream_op_batch_finish_with_failure(
+        batch,
+        grpc_error_set_int(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+                               "Established channel does not have a sufficient "
+                               "security level to transfer call credential."),
+                           GRPC_ERROR_INT_GRPC_STATUS,
+                           GRPC_STATUS_UNAUTHENTICATED),
+        calld->call_combiner);
+    return;
+  }
+
   grpc_auth_metadata_context_build(
       chand->security_connector->url_scheme(), calld->host, calld->method,
       chand->auth_context.get(), &calld->auth_md_context);

src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc

@@ -86,7 +86,7 @@ static tsi_result handshaker_result_extract_peer(
   alts_tsi_handshaker_result* result =
       reinterpret_cast<alts_tsi_handshaker_result*>(
           const_cast<tsi_handshaker_result*>(self));
-  GPR_ASSERT(kTsiAltsNumOfPeerProperties == 4);
+  GPR_ASSERT(kTsiAltsNumOfPeerProperties == 5);
   tsi_result ok = tsi_construct_peer(kTsiAltsNumOfPeerProperties, peer);
   int index = 0;
   if (ok != TSI_OK) {
@@ -131,6 +131,16 @@ static tsi_result handshaker_result_extract_peer(
     tsi_peer_destruct(peer);
     gpr_log(GPR_ERROR, "Failed to set tsi peer property");
   }
+  index++;
+  GPR_ASSERT(&peer->properties[index] != nullptr);
+  ok = tsi_construct_string_peer_property_from_cstring(
+      TSI_SECURITY_LEVEL_PEER_PROPERTY,
+      tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+      &peer->properties[index]);
+  if (ok != TSI_OK) {
+    tsi_peer_destruct(peer);
+    gpr_log(GPR_ERROR, "Failed to set tsi peer property");
+  }
   GPR_ASSERT(++index == kTsiAltsNumOfPeerProperties);
   return ok;
 }

src/core/tsi/alts/handshaker/alts_tsi_handshaker.h

@@ -36,7 +36,7 @@
 #define TSI_ALTS_RPC_VERSIONS "rpc_versions"
 #define TSI_ALTS_CONTEXT "alts_context"
 
-const size_t kTsiAltsNumOfPeerProperties = 4;
+const size_t kTsiAltsNumOfPeerProperties = 5;
 
 typedef struct alts_tsi_handshaker alts_tsi_handshaker;
 

src/core/tsi/fake_transport_security.cc

@@ -495,14 +495,18 @@ typedef struct {
 } fake_handshaker_result;
 
 static tsi_result fake_handshaker_result_extract_peer(
-    const tsi_handshaker_result* /*self*/, tsi_peer* peer) {
-  /* Construct a tsi_peer with 1 property: certificate type. */
-  tsi_result result = tsi_construct_peer(1, peer);
+    const tsi_handshaker_result* self, tsi_peer* peer) {
+  /* Construct a tsi_peer with 1 property: certificate type, security_level. */
+  tsi_result result = tsi_construct_peer(2, peer);
   if (result != TSI_OK) return result;
   result = tsi_construct_string_peer_property_from_cstring(
       TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_FAKE_CERTIFICATE_TYPE,
       &peer->properties[0]);
   if (result != TSI_OK) tsi_peer_destruct(peer);
+  result = tsi_construct_string_peer_property_from_cstring(
+      TSI_SECURITY_LEVEL_PEER_PROPERTY,
+      tsi_security_level_to_string(TSI_SECURITY_NONE), &peer->properties[1]);
+  if (result != TSI_OK) tsi_peer_destruct(peer);
   return result;
 }
 

src/core/tsi/fake_transport_security.h

@@ -25,6 +25,8 @@
 
 /* Value for the TSI_CERTIFICATE_TYPE_PEER_PROPERTY property for FAKE certs. */
 #define TSI_FAKE_CERTIFICATE_TYPE "FAKE"
+/* Value of the TSI_SECURITY_LEVEL_PEER_PROPERTY property for FAKE certs. */
+#define TSI_FAKE_SECURITY_LEVEL "TSI_SECURITY_NONE"
 
 /* Creates a fake handshaker that will create a fake frame protector.
 

src/core/tsi/ssl_transport_security.cc

@@ -1049,7 +1049,7 @@ static tsi_result ssl_handshaker_result_extract_peer(
   }
 
   // 1 is for session reused property.
-  size_t new_property_count = peer->property_count + 1;
+  size_t new_property_count = peer->property_count + 2;
   if (alpn_selected != nullptr) new_property_count++;
   tsi_peer_property* new_properties = static_cast<tsi_peer_property*>(
       gpr_zalloc(sizeof(*new_properties) * new_property_count));
@@ -1067,6 +1067,13 @@ static tsi_result ssl_handshaker_result_extract_peer(
     if (result != TSI_OK) return result;
     peer->property_count++;
   }
+  // Add security_level peer property.
+  result = tsi_construct_string_peer_property_from_cstring(
+      TSI_SECURITY_LEVEL_PEER_PROPERTY,
+      tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+      &peer->properties[peer->property_count]);
+  if (result != TSI_OK) return result;
+  peer->property_count++;
 
   const char* session_reused = SSL_session_reused(impl->ssl) ? "true" : "false";
   result = tsi_construct_string_peer_property_from_cstring(

src/core/tsi/transport_security.cc

@@ -67,6 +67,19 @@ const char* tsi_result_to_string(tsi_result result) {
   }
 }
 
+const char* tsi_security_level_to_string(tsi_security_level security_level) {
+  switch (security_level) {
+    case TSI_SECURITY_NONE:
+      return "TSI_SECURITY_NONE";
+    case TSI_INTEGRITY_ONLY:
+      return "TSI_INTEGRITY_ONLY";
+    case TSI_PRIVACY_AND_INTEGRITY:
+      return "TSI_PRIVACY_AND_INTEGRITY";
+    default:
+      return "UNKNOWN";
+  }
+}
+
 /* --- tsi_frame_protector common implementation. ---
 
    Calls specific implementation after state/input validation. */

src/core/tsi/transport_security_interface.h

@@ -46,6 +46,14 @@ typedef enum {
   TSI_HANDSHAKE_SHUTDOWN = 14,
 } tsi_result;
 
+typedef enum {
+  TSI_SECURITY_MIN,
+  TSI_SECURITY_NONE = TSI_SECURITY_MIN,
+  TSI_INTEGRITY_ONLY,
+  TSI_PRIVACY_AND_INTEGRITY,
+  TSI_SECURITY_MAX = TSI_PRIVACY_AND_INTEGRITY,
+} tsi_security_level;
+
 typedef enum {
   // Default option
   TSI_DONT_REQUEST_CLIENT_CERTIFICATE,
@@ -56,6 +64,7 @@ typedef enum {
 } tsi_client_certificate_request_type;
 
 const char* tsi_result_to_string(tsi_result result);
+const char* tsi_security_level_to_string(tsi_security_level security_level);
 
 /* --- tsi tracing --- */
 
@@ -185,6 +194,9 @@ void tsi_frame_protector_destroy(tsi_frame_protector* self);
 /* This property is of type TSI_PEER_PROPERTY_STRING.  */
 #define TSI_CERTIFICATE_TYPE_PEER_PROPERTY "certificate_type"
 
+/* This property represents security level of a channel. */
+#define TSI_SECURITY_LEVEL_PEER_PROPERTY "security_level"
+
 /* Property values may contain NULL characters just like C++ strings.
    The length field gives the length of the string. */
 typedef struct tsi_peer_property {

src/cpp/client/secure_credentials.cc

@@ -256,6 +256,20 @@ std::shared_ptr<CallCredentials> StsCredentials(
   return WrapCallCredentials(grpc_sts_credentials_create(&opts, nullptr));
 }
 
+std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
+    std::unique_ptr<MetadataCredentialsPlugin> plugin,
+    grpc_security_level min_security_level) {
+  grpc::GrpcLibraryCodegen init;  // To call grpc_init().
+  const char* type = plugin->GetType();
+  grpc::MetadataCredentialsPluginWrapper* wrapper =
+      new grpc::MetadataCredentialsPluginWrapper(std::move(plugin));
+  grpc_metadata_credentials_plugin c_plugin = {
+      grpc::MetadataCredentialsPluginWrapper::GetMetadata,
+      grpc::MetadataCredentialsPluginWrapper::Destroy, wrapper, type};
+  return WrapCallCredentials(grpc_metadata_credentials_create_from_plugin(
+      c_plugin, min_security_level, nullptr));
+}
+
 // Builds ALTS Credentials given ALTS specific options
 std::shared_ptr<ChannelCredentials> AltsCredentials(
     const AltsCredentialsOptions& options) {
@@ -374,8 +388,8 @@ std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
   grpc_metadata_credentials_plugin c_plugin = {
       grpc::MetadataCredentialsPluginWrapper::GetMetadata,
       grpc::MetadataCredentialsPluginWrapper::Destroy, wrapper, type};
-  return WrapCallCredentials(
-      grpc_metadata_credentials_create_from_plugin(c_plugin, nullptr));
+  return WrapCallCredentials(grpc_metadata_credentials_create_from_plugin(
+      c_plugin, GRPC_PRIVACY_AND_INTEGRITY, nullptr));
 }
 
 }  // namespace grpc_impl

src/csharp/ext/grpc_csharp_ext.c

@@ -1136,7 +1136,11 @@ grpcsharp_metadata_credentials_create_from_plugin(void* callback_tag) {
   plugin.destroy = grpcsharp_metadata_credentials_destroy_handler;
   plugin.state = callback_tag;
   plugin.type = "";
-  return grpc_metadata_credentials_create_from_plugin(plugin, NULL);
+  // TODO(yihuazhang): Expose min_security_level via the C# API so
+  // that applications can decide what minimum security level their
+  // plugins require.
+  return grpc_metadata_credentials_create_from_plugin(
+      plugin, GRPC_PRIVACY_AND_INTEGRITY, NULL);
 }
 
 /* Auth context */

src/php/ext/grpc/call_credentials.c

@@ -126,9 +126,10 @@ PHP_METHOD(CallCredentials, createFromPlugin) {
   plugin.destroy = plugin_destroy_state;
   plugin.state = (void *)state;
   plugin.type = "";
-
+  // TODO(yihuazhang): Expose min_security_level via the PHP API so that
+  // applications can decide what minimum security level their plugins require.
   grpc_call_credentials *creds =
-    grpc_metadata_credentials_create_from_plugin(plugin, NULL);
+    grpc_metadata_credentials_create_from_plugin(plugin, GRPC_PRIVACY_AND_INTEGRITY, NULL);
   zval *creds_object = grpc_php_wrap_call_credentials(creds TSRMLS_CC);
   RETURN_DESTROY_ZVAL(creds_object);
 }

src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi

@@ -76,7 +76,9 @@ cdef class MetadataPluginCallCredentials(CallCredentials):
     c_metadata_plugin.type = self._name
     cpython.Py_INCREF(self._metadata_plugin)
     fork_handlers_and_grpc_init()
-    return grpc_metadata_credentials_create_from_plugin(c_metadata_plugin, NULL)
+    # TODO(yihuazhang): Expose min_security_level via the Python API so that
+    # applications can decide what minimum security level their plugins require.
+    return grpc_metadata_credentials_create_from_plugin(c_metadata_plugin, GRPC_PRIVACY_AND_INTEGRITY, NULL)
 
 
 cdef grpc_call_credentials *_composition(call_credentialses):

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

@@ -433,6 +433,13 @@ cdef extern from "grpc/grpc_security.h":
     GRPC_SSL_REQUEST_AND_REQUIRE_CLIENT_CERTIFICATE_BUT_DONT_VERIFY
     GRPC_SSL_REQUEST_AND_REQUIRE_CLIENT_CERTIFICATE_AND_VERIFY
 
+  ctypedef enum grpc_security_level:
+    GRPC_SECURITY_MIN
+    GRPC_SECURITY_NONE = GRPC_SECURITY_MIN
+    GRPC_INTEGRITY_ONLY
+    GRPC_PRIVACY_AND_INTEGRITY
+    GRPC_SECURITY_MAX = GRPC_PRIVACY_AND_INTEGRITY
+
   ctypedef enum grpc_ssl_certificate_config_reload_status:
     GRPC_SSL_CERTIFICATE_CONFIG_RELOAD_UNCHANGED
     GRPC_SSL_CERTIFICATE_CONFIG_RELOAD_NEW
@@ -562,7 +569,7 @@ cdef extern from "grpc/grpc_security.h":
     const char *type
 
   grpc_call_credentials *grpc_metadata_credentials_create_from_plugin(
-      grpc_metadata_credentials_plugin plugin, void *reserved) nogil
+      grpc_metadata_credentials_plugin plugin, grpc_security_level min_security_level, void *reserved) nogil
 
   ctypedef struct grpc_auth_property_iterator:
     pass

src/python/grpcio_tests/tests/unit/_auth_context_test.py

@@ -103,11 +103,11 @@ class AuthContextTest(unittest.TestCase):
         auth_data = pickle.loads(response)
         self.assertIsNone(auth_data[_ID])
         self.assertIsNone(auth_data[_ID_KEY])
-        self.assertDictEqual(
-            {
-                'transport_security_type': [b'ssl'],
-                'ssl_session_reused': [b'false'],
-            }, auth_data[_AUTH_CTX])
+        self.assertDictEqual({
+            'security_level': [b'TSI_PRIVACY_AND_INTEGRITY'],
+            'transport_security_type': [b'ssl'],
+            'ssl_session_reused': [b'false'],
+        }, auth_data[_AUTH_CTX])
 
     def testSecureClientCert(self):
         handler = grpc.method_handlers_generic_handler('test', {

src/ruby/ext/grpc/rb_call_credentials.c

@@ -229,7 +229,10 @@ static VALUE grpc_rb_call_credentials_init(VALUE self, VALUE proc) {
   plugin.state = (void*)proc;
   plugin.type = "";
 
-  creds = grpc_metadata_credentials_create_from_plugin(plugin, NULL);
+  // TODO(yihuazhang): Expose min_security_level via the Ruby API so that
+  // applications can decide what minimum security level their plugins require.
+  creds = grpc_metadata_credentials_create_from_plugin(
+      plugin, GRPC_PRIVACY_AND_INTEGRITY, NULL);
   if (creds == NULL) {
     rb_raise(rb_eRuntimeError, "could not create a credentials, not sure why");
     return Qnil;

src/ruby/ext/grpc/rb_grpc_imports.generated.h

@@ -380,7 +380,7 @@ extern grpc_google_iam_credentials_create_type grpc_google_iam_credentials_creat
 typedef grpc_call_credentials*(*grpc_sts_credentials_create_type)(const grpc_sts_credentials_options* options, void* reserved);
 extern grpc_sts_credentials_create_type grpc_sts_credentials_create_import;
 #define grpc_sts_credentials_create grpc_sts_credentials_create_import
-typedef grpc_call_credentials*(*grpc_metadata_credentials_create_from_plugin_type)(grpc_metadata_credentials_plugin plugin, void* reserved);
+typedef grpc_call_credentials*(*grpc_metadata_credentials_create_from_plugin_type)(grpc_metadata_credentials_plugin plugin, grpc_security_level min_security_level, void* reserved);
 extern grpc_metadata_credentials_create_from_plugin_type grpc_metadata_credentials_create_from_plugin_import;
 #define grpc_metadata_credentials_create_from_plugin grpc_metadata_credentials_create_from_plugin_import
 typedef grpc_channel*(*grpc_secure_channel_create_type)(grpc_channel_credentials* creds, const char* target, const grpc_channel_args* args, void* reserved);

test/core/end2end/end2end_tests.h

@@ -34,6 +34,7 @@ typedef struct grpc_end2end_test_config grpc_end2end_test_config;
 #define FEATURE_MASK_DOES_NOT_SUPPORT_RESOURCE_QUOTA_SERVER 64
 #define FEATURE_MASK_DOES_NOT_SUPPORT_NETWORK_STATUS_CHANGE 128
 #define FEATURE_MASK_SUPPORTS_WORKAROUNDS 256
+#define FEATURE_MASK_DOES_NOT_SUPPORT_SEND_CALL_CREDENTIALS 512
 
 #define FAIL_AUTH_CHECK_SERVER_ARG_NAME "fail_auth_check"
 

test/core/end2end/fixtures/h2_fakesec.cc

@@ -130,7 +130,8 @@ static grpc_end2end_test_config configs[] = {
     {"chttp2/fake_secure_fullstack",
      FEATURE_MASK_SUPPORTS_DELAYED_CONNECTION |
          FEATURE_MASK_SUPPORTS_CLIENT_CHANNEL |
-         FEATURE_MASK_SUPPORTS_AUTHORITY_HEADER,
+         FEATURE_MASK_SUPPORTS_AUTHORITY_HEADER |
+         FEATURE_MASK_DOES_NOT_SUPPORT_SEND_CALL_CREDENTIALS,
      nullptr, chttp2_create_fixture_secure_fullstack,
      chttp2_init_client_fake_secure_fullstack,
      chttp2_init_server_fake_secure_fullstack,

test/core/end2end/tests/call_creds.cc

@@ -36,7 +36,7 @@ static const char iam_selector[] = "selector";
 static const char overridden_iam_token[] = "overridden_token";
 static const char overridden_iam_selector[] = "overridden_selector";
 
-typedef enum { NONE, OVERRIDE, DESTROY } override_mode;
+typedef enum { NONE, OVERRIDE, DESTROY, FAIL } override_mode;
 
 static void* tag(intptr_t t) { return (void*)t; }
 
@@ -174,6 +174,7 @@ static void request_response_with_payload_and_call_creds(
       GPR_ASSERT(grpc_call_set_credentials(c, creds) == GRPC_CALL_OK);
       break;
     case DESTROY:
+    case FAIL:
       GPR_ASSERT(grpc_call_set_credentials(c, nullptr) == GRPC_CALL_OK);
       break;
   }
@@ -312,6 +313,7 @@ static void request_response_with_payload_and_call_creds(
                                    overridden_iam_selector));
       break;
     case DESTROY:
+    case FAIL:
       GPR_ASSERT(!contains_metadata(&request_metadata_recv,
                                     GRPC_IAM_AUTHORIZATION_TOKEN_METADATA_KEY,
                                     iam_token));
@@ -367,6 +369,13 @@ static void test_request_response_with_payload_and_deleted_call_creds(
       DESTROY);
 }
 
+static void test_request_response_with_payload_fail_to_send_call_creds(
+    grpc_end2end_test_config config) {
+  request_response_with_payload_and_call_creds(
+      "test_request_response_with_payload_fail_to_send_call_creds", config,
+      FAIL);
+}
+
 static void test_request_with_server_rejecting_client_creds(
     grpc_end2end_test_config config) {
   grpc_op ops[6];
@@ -472,6 +481,10 @@ void call_creds(grpc_end2end_test_config config) {
     test_request_response_with_payload_and_deleted_call_creds(config);
     test_request_with_server_rejecting_client_creds(config);
   }
+  if (config.feature_mask &
+      FEATURE_MASK_DOES_NOT_SUPPORT_SEND_CALL_CREDENTIALS) {
+    test_request_response_with_payload_fail_to_send_call_creds(config);
+  }
 }
 
 void call_creds_pre_init(void) {}

test/core/security/alts_security_connector_test.cc

@@ -74,6 +74,39 @@ static void test_missing_rpc_protocol_versions_property_failure() {
   tsi_peer_destruct(&peer);
 }
 
+static void test_missing_security_level_property_failure() {
+  tsi_peer peer;
+  GPR_ASSERT(tsi_construct_peer(kTsiAltsNumOfPeerProperties, &peer) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_ALTS_CERTIFICATE_TYPE,
+                 &peer.properties[0]) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_ALTS_SERVICE_ACCOUNT_PEER_PROPERTY, "alice",
+                 &peer.properties[1]) == TSI_OK);
+  grpc_gcp_rpc_protocol_versions peer_versions;
+  grpc_gcp_rpc_protocol_versions_set_max(&peer_versions,
+                                         GRPC_PROTOCOL_VERSION_MAX_MAJOR,
+                                         GRPC_PROTOCOL_VERSION_MAX_MINOR);
+  grpc_gcp_rpc_protocol_versions_set_min(&peer_versions,
+                                         GRPC_PROTOCOL_VERSION_MIN_MAJOR,
+                                         GRPC_PROTOCOL_VERSION_MIN_MINOR);
+  grpc_slice serialized_peer_versions;
+  GPR_ASSERT(grpc_gcp_rpc_protocol_versions_encode(&peer_versions,
+                                                   &serialized_peer_versions));
+
+  GPR_ASSERT(tsi_construct_string_peer_property(
+                 TSI_ALTS_RPC_VERSIONS,
+                 reinterpret_cast<char*>(
+                     GRPC_SLICE_START_PTR(serialized_peer_versions)),
+                 GRPC_SLICE_LENGTH(serialized_peer_versions),
+                 &peer.properties[2]) == TSI_OK);
+  grpc_core::RefCountedPtr<grpc_auth_context> ctx =
+      grpc_alts_auth_context_from_tsi_peer(&peer);
+  GPR_ASSERT(ctx == nullptr);
+  grpc_slice_unref(serialized_peer_versions);
+  tsi_peer_destruct(&peer);
+}
+
 static void test_unknown_peer_property_failure() {
   tsi_peer peer;
   GPR_ASSERT(tsi_construct_peer(kTsiAltsNumOfPeerProperties, &peer) == TSI_OK);
@@ -135,6 +168,10 @@ static void test_alts_peer_to_auth_context_success() {
                      GRPC_SLICE_START_PTR(serialized_peer_versions)),
                  GRPC_SLICE_LENGTH(serialized_peer_versions),
                  &peer.properties[2]) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_SECURITY_LEVEL_PEER_PROPERTY,
+                 tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+                 &peer.properties[3]) == TSI_OK);
   char test_ctx[] = "test serialized context";
   grpc_slice serialized_alts_ctx = grpc_slice_from_copied_string(test_ctx);
   GPR_ASSERT(
@@ -142,7 +179,7 @@ static void test_alts_peer_to_auth_context_success() {
           TSI_ALTS_CONTEXT,
           reinterpret_cast<char*>(GRPC_SLICE_START_PTR(serialized_alts_ctx)),
           GRPC_SLICE_LENGTH(serialized_alts_ctx),
-          &peer.properties[3]) == TSI_OK);
+          &peer.properties[4]) == TSI_OK);
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_alts_auth_context_from_tsi_peer(&peer);
   GPR_ASSERT(ctx != nullptr);
@@ -161,6 +198,7 @@ int main(int /*argc*/, char** /*argv*/) {
   test_empty_peer_property_failure();
   test_unknown_peer_property_failure();
   test_missing_rpc_protocol_versions_property_failure();
+  test_missing_security_level_property_failure();
   test_alts_peer_to_auth_context_success();
 
   return 0;

test/core/security/credentials_test.cc

@@ -404,6 +404,8 @@ static void test_google_iam_creds(void) {
   grpc_call_credentials* creds = grpc_google_iam_credentials_create(
       test_google_iam_authorization_token, test_google_iam_authority_selector,
       nullptr);
+  /* Check security level. */
+  GPR_ASSERT(creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
   grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method,
                                             nullptr, nullptr};
   run_request_metadata_test(creds, auth_md_ctx, state);
@@ -420,6 +422,8 @@ static void test_access_token_creds(void) {
   grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method,
                                             nullptr, nullptr};
   GPR_ASSERT(strcmp(creds->type(), GRPC_CALL_CREDENTIALS_TYPE_OAUTH2) == 0);
+  /* Check security level. */
+  GPR_ASSERT(creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
   run_request_metadata_test(creds, auth_md_ctx, state);
   creds->Unref();
 }
@@ -474,12 +478,20 @@ static void test_oauth2_google_iam_composite_creds(void) {
                                             nullptr, nullptr};
   grpc_call_credentials* oauth2_creds = grpc_md_only_test_credentials_create(
       "authorization", test_oauth2_bearer_token, 0);
+
+  /* Check security level of fake credentials. */
+  GPR_ASSERT(oauth2_creds->min_security_level() == GRPC_SECURITY_NONE);
+
   grpc_call_credentials* google_iam_creds = grpc_google_iam_credentials_create(
       test_google_iam_authorization_token, test_google_iam_authority_selector,
       nullptr);
   grpc_call_credentials* composite_creds =
       grpc_composite_call_credentials_create(oauth2_creds, google_iam_creds,
                                              nullptr);
+  /* Check security level of composite credentials. */
+  GPR_ASSERT(composite_creds->min_security_level() ==
+             GRPC_PRIVACY_AND_INTEGRITY);
+
   oauth2_creds->Unref();
   google_iam_creds->Unref();
   GPR_ASSERT(strcmp(composite_creds->type(),
@@ -536,6 +548,7 @@ static void test_channel_oauth2_google_iam_composite_creds(void) {
   grpc_call_credentials* google_iam_creds = grpc_google_iam_credentials_create(
       test_google_iam_authorization_token, test_google_iam_authority_selector,
       nullptr);
+
   grpc_channel_credentials* channel_oauth2_iam_creds =
       grpc_composite_channel_credentials_create(channel_oauth2_creds,
                                                 google_iam_creds, nullptr);
@@ -604,6 +617,8 @@ static void test_compute_engine_creds_success() {
       grpc_google_compute_engine_credentials_create(nullptr);
   grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method,
                                             nullptr, nullptr};
+  /* Check security level. */
+  GPR_ASSERT(creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
 
   /* First request: http get should be called. */
   request_metadata_state* state =
@@ -695,6 +710,9 @@ static void test_refresh_token_creds_success(void) {
   grpc_call_credentials* creds = grpc_google_refresh_token_credentials_create(
       test_refresh_token_str, nullptr);
 
+  /* Check security level. */
+  GPR_ASSERT(creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
+
   /* First request: http put should be called. */
   request_metadata_state* state =
       make_request_metadata_state(GRPC_ERROR_NONE, emd, GPR_ARRAY_SIZE(emd));
@@ -924,6 +942,9 @@ static void test_sts_creds_success(void) {
   grpc_call_credentials* creds =
       grpc_sts_credentials_create(&valid_options, nullptr);
 
+  /* Check security level. */
+  GPR_ASSERT(creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
+
   /* First request: http put should be called. */
   request_metadata_state* state =
       make_request_metadata_state(GRPC_ERROR_NONE, emd, GPR_ARRAY_SIZE(emd));
@@ -1067,6 +1088,8 @@ static void test_jwt_creds_lifetime(void) {
           json_key_string, grpc_max_auth_token_lifetime(), nullptr);
   GPR_ASSERT(gpr_time_cmp(creds_as_jwt(jwt_creds)->jwt_lifetime(),
                           grpc_max_auth_token_lifetime()) == 0);
+  /* Check security level. */
+  GPR_ASSERT(jwt_creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
   grpc_call_credentials_release(jwt_creds);
 
   // Shorter lifetime.
@@ -1408,8 +1431,10 @@ static void test_metadata_plugin_success(void) {
   plugin.get_metadata = plugin_get_metadata_success;
   plugin.destroy = plugin_destroy;
 
-  grpc_call_credentials* creds =
-      grpc_metadata_credentials_create_from_plugin(plugin, nullptr);
+  grpc_call_credentials* creds = grpc_metadata_credentials_create_from_plugin(
+      plugin, GRPC_PRIVACY_AND_INTEGRITY, nullptr);
+  /* Check security level. */
+  GPR_ASSERT(creds->min_security_level() == GRPC_PRIVACY_AND_INTEGRITY);
   GPR_ASSERT(state == PLUGIN_INITIAL_STATE);
   run_request_metadata_test(creds, auth_md_ctx, md_state);
   GPR_ASSERT(state == PLUGIN_GET_METADATA_CALLED_STATE);
@@ -1436,8 +1461,8 @@ static void test_metadata_plugin_failure(void) {
   plugin.get_metadata = plugin_get_metadata_failure;
   plugin.destroy = plugin_destroy;
 
-  grpc_call_credentials* creds =
-      grpc_metadata_credentials_create_from_plugin(plugin, nullptr);
+  grpc_call_credentials* creds = grpc_metadata_credentials_create_from_plugin(
+      plugin, GRPC_PRIVACY_AND_INTEGRITY, nullptr);
   GPR_ASSERT(state == PLUGIN_INITIAL_STATE);
   run_request_metadata_test(creds, auth_md_ctx, md_state);
   GPR_ASSERT(state == PLUGIN_GET_METADATA_CALLED_STATE);

test/core/security/security_connector_test.cc

@@ -84,13 +84,38 @@ static int check_ssl_peer_equivalence(const tsi_peer* original,
   return 1;
 }
 
+static void test_check_security_level() {
+  GPR_ASSERT(grpc_check_security_level(GRPC_PRIVACY_AND_INTEGRITY,
+                                       GRPC_PRIVACY_AND_INTEGRITY) == true);
+  GPR_ASSERT(grpc_check_security_level(GRPC_PRIVACY_AND_INTEGRITY,
+                                       GRPC_INTEGRITY_ONLY) == true);
+  GPR_ASSERT(grpc_check_security_level(GRPC_PRIVACY_AND_INTEGRITY,
+                                       GRPC_SECURITY_NONE) == true);
+  GPR_ASSERT(grpc_check_security_level(GRPC_INTEGRITY_ONLY,
+                                       GRPC_PRIVACY_AND_INTEGRITY) == false);
+  GPR_ASSERT(grpc_check_security_level(GRPC_INTEGRITY_ONLY,
+                                       GRPC_INTEGRITY_ONLY) == true);
+  GPR_ASSERT(grpc_check_security_level(GRPC_INTEGRITY_ONLY,
+                                       GRPC_SECURITY_NONE) == true);
+  GPR_ASSERT(grpc_check_security_level(GRPC_SECURITY_NONE,
+                                       GRPC_PRIVACY_AND_INTEGRITY) == false);
+  GPR_ASSERT(grpc_check_security_level(GRPC_SECURITY_NONE,
+                                       GRPC_INTEGRITY_ONLY) == false);
+  GPR_ASSERT(grpc_check_security_level(GRPC_SECURITY_NONE,
+                                       GRPC_SECURITY_NONE) == true);
+}
+
 static void test_unauthenticated_ssl_peer(void) {
   tsi_peer peer;
   tsi_peer rpeer;
-  GPR_ASSERT(tsi_construct_peer(1, &peer) == TSI_OK);
+  GPR_ASSERT(tsi_construct_peer(2, &peer) == TSI_OK);
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_X509_CERTIFICATE_TYPE,
                  &peer.properties[0]) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_SECURITY_LEVEL_PEER_PROPERTY,
+                 tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+                 &peer.properties[1]) == TSI_OK);
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_ssl_peer_to_auth_context(&peer, GRPC_SSL_TRANSPORT_SECURITY_TYPE);
   GPR_ASSERT(ctx != nullptr);
@@ -181,7 +206,7 @@ static void test_cn_only_ssl_peer_to_auth_context(void) {
   tsi_peer rpeer;
   const char* expected_cn = "cn1";
   const char* expected_pem_cert = "pem_cert1";
-  GPR_ASSERT(tsi_construct_peer(3, &peer) == TSI_OK);
+  GPR_ASSERT(tsi_construct_peer(4, &peer) == TSI_OK);
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_X509_CERTIFICATE_TYPE,
                  &peer.properties[0]) == TSI_OK);
@@ -191,6 +216,11 @@ static void test_cn_only_ssl_peer_to_auth_context(void) {
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_X509_PEM_CERT_PROPERTY, expected_pem_cert,
                  &peer.properties[2]) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_SECURITY_LEVEL_PEER_PROPERTY,
+                 tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+                 &peer.properties[3]) == TSI_OK);
+
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_ssl_peer_to_auth_context(&peer, GRPC_SSL_TRANSPORT_SECURITY_TYPE);
   GPR_ASSERT(ctx != nullptr);
@@ -215,7 +245,7 @@ static void test_cn_and_one_san_ssl_peer_to_auth_context(void) {
   const char* expected_cn = "cn1";
   const char* expected_san = "san1";
   const char* expected_pem_cert = "pem_cert1";
-  GPR_ASSERT(tsi_construct_peer(4, &peer) == TSI_OK);
+  GPR_ASSERT(tsi_construct_peer(5, &peer) == TSI_OK);
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_X509_CERTIFICATE_TYPE,
                  &peer.properties[0]) == TSI_OK);
@@ -228,7 +258,10 @@ static void test_cn_and_one_san_ssl_peer_to_auth_context(void) {
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_X509_PEM_CERT_PROPERTY, expected_pem_cert,
                  &peer.properties[3]) == TSI_OK);
-
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_SECURITY_LEVEL_PEER_PROPERTY,
+                 tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+                 &peer.properties[4]) == TSI_OK);
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_ssl_peer_to_auth_context(&peer, GRPC_SSL_TRANSPORT_SECURITY_TYPE);
   GPR_ASSERT(ctx != nullptr);
@@ -254,7 +287,7 @@ static void test_cn_and_multiple_sans_ssl_peer_to_auth_context(void) {
   const char* expected_sans[] = {"san1", "san2", "san3"};
   const char* expected_pem_cert = "pem_cert1";
   size_t i;
-  GPR_ASSERT(tsi_construct_peer(3 + GPR_ARRAY_SIZE(expected_sans), &peer) ==
+  GPR_ASSERT(tsi_construct_peer(4 + GPR_ARRAY_SIZE(expected_sans), &peer) ==
              TSI_OK);
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_X509_CERTIFICATE_TYPE,
@@ -265,10 +298,14 @@ static void test_cn_and_multiple_sans_ssl_peer_to_auth_context(void) {
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_X509_PEM_CERT_PROPERTY, expected_pem_cert,
                  &peer.properties[2]) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_SECURITY_LEVEL_PEER_PROPERTY,
+                 tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+                 &peer.properties[3]) == TSI_OK);
   for (i = 0; i < GPR_ARRAY_SIZE(expected_sans); i++) {
     GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                    TSI_X509_SUBJECT_ALTERNATIVE_NAME_PEER_PROPERTY,
-                   expected_sans[i], &peer.properties[3 + i]) == TSI_OK);
+                   expected_sans[i], &peer.properties[4 + i]) == TSI_OK);
   }
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_ssl_peer_to_auth_context(&peer, GRPC_SSL_TRANSPORT_SECURITY_TYPE);
@@ -296,7 +333,7 @@ static void test_cn_and_multiple_sans_and_others_ssl_peer_to_auth_context(
   const char* expected_pem_cert = "pem_cert1";
   const char* expected_sans[] = {"san1", "san2", "san3"};
   size_t i;
-  GPR_ASSERT(tsi_construct_peer(5 + GPR_ARRAY_SIZE(expected_sans), &peer) ==
+  GPR_ASSERT(tsi_construct_peer(6 + GPR_ARRAY_SIZE(expected_sans), &peer) ==
              TSI_OK);
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_X509_CERTIFICATE_TYPE,
@@ -311,10 +348,14 @@ static void test_cn_and_multiple_sans_and_others_ssl_peer_to_auth_context(
   GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                  TSI_X509_PEM_CERT_PROPERTY, expected_pem_cert,
                  &peer.properties[4]) == TSI_OK);
+  GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
+                 TSI_SECURITY_LEVEL_PEER_PROPERTY,
+                 tsi_security_level_to_string(TSI_PRIVACY_AND_INTEGRITY),
+                 &peer.properties[5]) == TSI_OK);
   for (i = 0; i < GPR_ARRAY_SIZE(expected_sans); i++) {
     GPR_ASSERT(tsi_construct_string_peer_property_from_cstring(
                    TSI_X509_SUBJECT_ALTERNATIVE_NAME_PEER_PROPERTY,
-                   expected_sans[i], &peer.properties[5 + i]) == TSI_OK);
+                   expected_sans[i], &peer.properties[6 + i]) == TSI_OK);
   }
   grpc_core::RefCountedPtr<grpc_auth_context> ctx =
       grpc_ssl_peer_to_auth_context(&peer, GRPC_SSL_TRANSPORT_SECURITY_TYPE);
@@ -485,6 +526,7 @@ int main(int argc, char** argv) {
   test_ipv6_address_san();
   test_default_ssl_roots();
   test_peer_alpn_check();
+  test_check_security_level();
   grpc_shutdown();
   return 0;
 }

test/core/tsi/alts/handshaker/alts_tsi_handshaker_test.cc

@@ -35,6 +35,7 @@
 #define ALTS_TSI_HANDSHAKER_TEST_CONSUMED_BYTES "Hello "
 #define ALTS_TSI_HANDSHAKER_TEST_REMAIN_BYTES "Google"
 #define ALTS_TSI_HANDSHAKER_TEST_PEER_IDENTITY "chapi@service.google.com"
+#define ALTS_TSI_HANDSHAKER_TEST_SECURITY_LEVEL "TSI_PRIVACY_AND_INTEGRITY"
 #define ALTS_TSI_HANDSHAKER_TEST_KEY_DATA \
   "ABCDEFGHIJKLMNOPABCDEFGHIJKLMNOPABCDEFGHIJKL"
 #define ALTS_TSI_HANDSHAKER_TEST_BUFFER_SIZE 100
@@ -309,6 +310,10 @@ static void on_client_next_success_cb(tsi_result status, void* user_data,
                     peer_account.size) == 0);
   GPR_ASSERT(memcmp(ALTS_TSI_HANDSHAKER_TEST_LOCAL_IDENTITY, local_account.data,
                     local_account.size) == 0);
+  /* Validate security level. */
+  GPR_ASSERT(memcmp(ALTS_TSI_HANDSHAKER_TEST_SECURITY_LEVEL,
+                    peer.properties[4].value.data,
+                    peer.properties[4].value.length) == 0);
   tsi_peer_destruct(&peer);
   /* Validate unused bytes. */
   const unsigned char* bytes = nullptr;
@@ -365,6 +370,11 @@ static void on_server_next_success_cb(tsi_result status, void* user_data,
                     peer_account.size) == 0);
   GPR_ASSERT(memcmp(ALTS_TSI_HANDSHAKER_TEST_LOCAL_IDENTITY, local_account.data,
                     local_account.size) == 0);
+  /* Check security level. */
+  GPR_ASSERT(memcmp(ALTS_TSI_HANDSHAKER_TEST_SECURITY_LEVEL,
+                    peer.properties[4].value.data,
+                    peer.properties[4].value.length) == 0);
+
   tsi_peer_destruct(&peer);
   /* Validate unused bytes. */
   const unsigned char* bytes = nullptr;

test/core/tsi/fake_transport_security_test.cc

@@ -50,6 +50,11 @@ static void validate_handshaker_peers(tsi_handshaker_result* result) {
   GPR_ASSERT(property != nullptr);
   GPR_ASSERT(memcmp(property->value.data, TSI_FAKE_CERTIFICATE_TYPE,
                     property->value.length) == 0);
+  property =
+      tsi_peer_get_property_by_name(&peer, TSI_SECURITY_LEVEL_PEER_PROPERTY);
+  GPR_ASSERT(property != nullptr);
+  GPR_ASSERT(memcmp(property->value.data, TSI_FAKE_SECURITY_LEVEL,
+                    property->value.length) == 0);
   tsi_peer_destruct(&peer);
 }
 

test/core/tsi/ssl_transport_security_test.cc

@@ -187,6 +187,15 @@ static void check_alpn(ssl_tsi_test_fixture* ssl_fixture,
   }
 }
 
+static void check_security_level(const tsi_peer* peer) {
+  const tsi_peer_property* security_level =
+      tsi_peer_get_property_by_name(peer, TSI_SECURITY_LEVEL_PEER_PROPERTY);
+  GPR_ASSERT(security_level != nullptr);
+  const char* expected_match = "TSI_PRIVACY_AND_INTEGRITY";
+  GPR_ASSERT(memcmp(security_level->value.data, expected_match,
+                    security_level->value.length) == 0);
+}
+
 static const tsi_peer_property*
 check_basic_authenticated_peer_and_get_common_name(const tsi_peer* peer) {
   const tsi_peer_property* cert_type_property =
@@ -271,7 +280,7 @@ static void check_client_peer(ssl_tsi_test_fixture* ssl_fixture,
   ssl_alpn_lib* alpn_lib = ssl_fixture->alpn_lib;
   if (!ssl_fixture->force_client_auth) {
     GPR_ASSERT(peer->property_count ==
-               (alpn_lib->alpn_mode == ALPN_CLIENT_SERVER_OK ? 2 : 1));
+               (alpn_lib->alpn_mode == ALPN_CLIENT_SERVER_OK ? 3 : 2));
   } else {
     const tsi_peer_property* property =
         check_basic_authenticated_peer_and_get_common_name(peer);
@@ -297,6 +306,7 @@ static void ssl_test_check_handshaker_peers(tsi_test_fixture* fixture) {
                    ssl_fixture->base.client_result, &peer) == TSI_OK);
     check_session_reusage(ssl_fixture, &peer);
     check_alpn(ssl_fixture, &peer);
+    check_security_level(&peer);
     if (ssl_fixture->server_name_indication != nullptr) {
       check_server1_peer(&peer);
     } else {
@@ -310,6 +320,7 @@ static void ssl_test_check_handshaker_peers(tsi_test_fixture* fixture) {
                    ssl_fixture->base.server_result, &peer) == TSI_OK);
     check_session_reusage(ssl_fixture, &peer);
     check_alpn(ssl_fixture, &peer);
+    check_security_level(&peer);
     check_client_peer(ssl_fixture, &peer);
   } else {
     GPR_ASSERT(ssl_fixture->base.server_result == nullptr);
@@ -825,7 +836,8 @@ void ssl_tsi_test_extract_x509_subject_names() {
   tsi_peer peer;
   GPR_ASSERT(tsi_ssl_extract_x509_subject_names_from_pem_cert(cert, &peer) ==
              TSI_OK);
-  // One for common name, one for certificate, and six for SAN fields.
+  // One for common name, one for certificate, one for security level, and six
+  // for SAN fields.
   size_t expected_property_count = 8;
   GPR_ASSERT(peer.property_count == expected_property_count);
   // Check common name