Update links to grpc.io guides in header files

include/grpcpp/grpcpp.h

@@ -21,7 +21,7 @@
 /// The gRPC C++ API mainly consists of the following classes:
 /// <br>
 /// - grpc::Channel, which represents the connection to an endpoint. See [the
-/// gRPC Concepts page](https://grpc.io/docs/guides/concepts.html) for more
+/// gRPC Concepts page](https://grpc.io/docs/what-is-grpc/core-concepts) for more
 /// details. Channels are created by the factory function grpc::CreateChannel.
 ///
 /// - grpc::CompletionQueue, the producer-consumer queue used for all

include/grpcpp/impl/codegen/client_context_impl.h

@@ -319,7 +319,7 @@ class ClientContext {
   ///
   /// It is legal to call this only before initial metadata is sent.
   ///
-  /// \see  https://grpc.io/docs/guides/auth.html
+  /// \see  https://grpc.io/docs/guides/auth
   void set_credentials(
       const std::shared_ptr<grpc_impl::CallCredentials>& creds);
 

include/grpcpp/security/credentials_impl.h

@@ -62,7 +62,7 @@ std::shared_ptr<Channel> CreateCustomChannelWithInterceptors(
 /// It can make various assertions, e.g., about the client’s identity, role
 /// for all the calls on that channel.
 ///
-/// \see https://grpc.io/docs/guides/auth.html
+/// \see https://grpc.io/docs/guides/auth
 class ChannelCredentials : private grpc::GrpcLibraryCodegen {
  public:
   ChannelCredentials();
@@ -107,7 +107,7 @@ class ChannelCredentials : private grpc::GrpcLibraryCodegen {
 /// A call credentials object encapsulates the state needed by a client to
 /// authenticate with a server for a given call on a channel.
 ///
-/// \see https://grpc.io/docs/guides/auth.html
+/// \see https://grpc.io/docs/guides/auth
 class CallCredentials : private grpc::GrpcLibraryCodegen {
  public:
   CallCredentials();