[context] Move security context to arena based context (#36783)

Closes #36783

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36783 from ctiller:ctx9 2ade190f45
PiperOrigin-RevId: 639096344

src/core/lib/channel/context.h

@@ -32,10 +32,6 @@ typedef enum {
   /// grpc_call* associated with this context.
   GRPC_CONTEXT_CALL = 0,
 
-  /// Value is either a \a grpc_client_security_context or a
-  /// \a grpc_server_security_context.
-  GRPC_CONTEXT_SECURITY,
-
   /// Value is a \a census_context.
   GRPC_CONTEXT_TRACING,
 

src/core/lib/security/context/security_context.cc

@@ -56,12 +56,12 @@ grpc_call_error grpc_call_set_credentials(grpc_call* call,
     LOG(ERROR) << "Method is client-side only.";
     return GRPC_CALL_ERROR_NOT_ON_SERVER;
   }
-  ctx = static_cast<grpc_client_security_context*>(
-      grpc_call_context_get(call, GRPC_CONTEXT_SECURITY));
+  auto* arena = grpc_call_get_arena(call);
+  ctx = grpc_core::DownCast<grpc_client_security_context*>(
+      arena->GetContext<grpc_core::SecurityContext>());
   if (ctx == nullptr) {
-    ctx = grpc_client_security_context_create(grpc_call_get_arena(call), creds);
-    grpc_call_context_set(call, GRPC_CONTEXT_SECURITY, ctx,
-                          grpc_client_security_context_destroy);
+    ctx = grpc_client_security_context_create(arena, creds);
+    arena->SetContext<grpc_core::SecurityContext>(ctx);
   } else {
     ctx->creds = creds != nullptr ? creds->Ref() : nullptr;
   }
@@ -70,11 +70,12 @@ grpc_call_error grpc_call_set_credentials(grpc_call* call,
 }
 
 grpc_auth_context* grpc_call_auth_context(grpc_call* call) {
-  void* sec_ctx = grpc_call_context_get(call, GRPC_CONTEXT_SECURITY);
+  auto* sec_ctx =
+      grpc_call_get_arena(call)->GetContext<grpc_core::SecurityContext>();
   GRPC_API_TRACE("grpc_call_auth_context(call=%p)", 1, (call));
   if (sec_ctx == nullptr) return nullptr;
   if (grpc_call_is_client(call)) {
-    auto* sc = static_cast<grpc_client_security_context*>(sec_ctx);
+    auto* sc = grpc_core::DownCast<grpc_client_security_context*>(sec_ctx);
     if (sc->auth_context == nullptr) {
       return nullptr;
     } else {
@@ -83,7 +84,7 @@ grpc_auth_context* grpc_call_auth_context(grpc_call* call) {
           .release();
     }
   } else {
-    auto* sc = static_cast<grpc_server_security_context*>(sec_ctx);
+    auto* sc = grpc_core::DownCast<grpc_server_security_context*>(sec_ctx);
     if (sc->auth_context == nullptr) {
       return nullptr;
     } else {

src/core/lib/security/context/security_context.h

@@ -136,15 +136,24 @@ struct grpc_security_context_extension {
   void (*destroy)(void*) = nullptr;
 };
 
+namespace grpc_core {
+
+class SecurityContext {
+ public:
+  virtual ~SecurityContext() = default;
+};
+
+}  // namespace grpc_core
+
 // --- grpc_client_security_context ---
 
 // Internal client-side security context.
 
-struct grpc_client_security_context {
+struct grpc_client_security_context final : public grpc_core::SecurityContext {
   explicit grpc_client_security_context(
       grpc_core::RefCountedPtr<grpc_call_credentials> creds)
       : creds(std::move(creds)) {}
-  ~grpc_client_security_context();
+  ~grpc_client_security_context() override;
 
   grpc_core::RefCountedPtr<grpc_call_credentials> creds;
   grpc_core::RefCountedPtr<grpc_auth_context> auth_context;
@@ -159,9 +168,9 @@ void grpc_client_security_context_destroy(void* ctx);
 
 // Internal server-side security context.
 
-struct grpc_server_security_context {
+struct grpc_server_security_context final : public grpc_core::SecurityContext {
   grpc_server_security_context() = default;
-  ~grpc_server_security_context();
+  ~grpc_server_security_context() override;
 
   grpc_core::RefCountedPtr<grpc_auth_context> auth_context;
   grpc_security_context_extension extension;
@@ -178,4 +187,20 @@ grpc_auth_context* grpc_auth_context_from_arg(const grpc_arg* arg);
 grpc_auth_context* grpc_find_auth_context_in_args(
     const grpc_channel_args* args);
 
+namespace grpc_core {
+template <>
+struct ArenaContextType<SecurityContext> {
+  static void Destroy(SecurityContext* p) { p->~SecurityContext(); }
+};
+
+template <>
+struct ContextSubclass<grpc_client_security_context> {
+  using Base = SecurityContext;
+};
+template <>
+struct ContextSubclass<grpc_server_security_context> {
+  using Base = SecurityContext;
+};
+}  // namespace grpc_core
+
 #endif  // GRPC_SRC_CORE_LIB_SECURITY_CONTEXT_SECURITY_CONTEXT_H

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

@@ -110,8 +110,7 @@ ClientAuthFilter::ClientAuthFilter(
 
 ArenaPromise<absl::StatusOr<CallArgs>> ClientAuthFilter::GetCallCredsMetadata(
     CallArgs call_args) {
-  auto* ctx = static_cast<grpc_client_security_context*>(
-      GetContext<grpc_call_context_element>()[GRPC_CONTEXT_SECURITY].value);
+  auto* ctx = GetContext<grpc_client_security_context>();
   grpc_call_credentials* channel_call_creds =
       args_.security_connector->mutable_request_metadata_creds();
   const bool call_creds_has_md = (ctx != nullptr) && (ctx->creds != nullptr);
@@ -178,17 +177,13 @@ ArenaPromise<absl::StatusOr<CallArgs>> ClientAuthFilter::GetCallCredsMetadata(
 
 ArenaPromise<ServerMetadataHandle> ClientAuthFilter::MakeCallPromise(
     CallArgs call_args, NextPromiseFactory next_promise_factory) {
-  auto* legacy_ctx = GetContext<grpc_call_context_element>();
-  if (legacy_ctx[GRPC_CONTEXT_SECURITY].value == nullptr) {
-    legacy_ctx[GRPC_CONTEXT_SECURITY].value =
-        grpc_client_security_context_create(GetContext<Arena>(),
+  auto* sec_ctx = MaybeGetContext<grpc_client_security_context>();
+  if (sec_ctx == nullptr) {
+    sec_ctx = grpc_client_security_context_create(GetContext<Arena>(),
                                                   /*creds=*/nullptr);
-    legacy_ctx[GRPC_CONTEXT_SECURITY].destroy =
-        grpc_client_security_context_destroy;
+    SetContext<SecurityContext>(sec_ctx);
   }
-  static_cast<grpc_client_security_context*>(
-      legacy_ctx[GRPC_CONTEXT_SECURITY].value)
-      ->auth_context = args_.auth_context;
+  sec_ctx->auth_context = args_.auth_context;
 
   auto* host =
       call_args.client_initial_metadata->get_pointer(HttpAuthorityMetadata());

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

@@ -203,11 +203,7 @@ ServerAuthFilter::Call::Call(ServerAuthFilter* filter) {
       grpc_server_security_context_create(GetContext<Arena>());
   server_ctx->auth_context =
       filter->auth_context_->Ref(DEBUG_LOCATION, "server_auth_filter");
-  grpc_call_context_element& context =
-      GetContext<grpc_call_context_element>()[GRPC_CONTEXT_SECURITY];
-  if (context.value != nullptr) context.destroy(context.value);
-  context.value = server_ctx;
-  context.destroy = grpc_server_security_context_destroy;
+  SetContext<SecurityContext>(server_ctx);
 }
 
 ServerAuthFilter::ServerAuthFilter(