[alts] Log host and target name on CheckCallHost failure. (#33028)

Having this logging will help debug a current failure.

BUILD

@@ -3156,6 +3156,7 @@ grpc_cc_library(
     external_deps = [
         "absl/status",
         "absl/strings",
+        "absl/strings:str_format",
         "absl/types:optional",
     ],
     language = "c++",

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

@@ -23,9 +23,11 @@
 #include <string.h>
 
 #include <algorithm>
+#include <initializer_list>
 #include <utility>
 
 #include "absl/status/status.h"
+#include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
 
@@ -132,8 +134,9 @@ class grpc_alts_channel_security_connector final
   grpc_core::ArenaPromise<absl::Status> CheckCallHost(
       absl::string_view host, grpc_auth_context*) override {
     if (host.empty() || host != target_name_) {
-      return grpc_core::Immediate(absl::UnauthenticatedError(
+      return grpc_core::Immediate(absl::UnauthenticatedError(absl::StrFormat(
-          "ALTS call host does not match target name"));
+          "ALTS call host [%s] does not match target name [%s].", host,
+          target_name_)));
     }
     return grpc_core::ImmediateOkStatus();
   }