Addressing comments.

include/grpc/grpc_security.h

src/core/channel/context.h

src/core/security/client_auth_filter.c

src/core/security/security_context.c

src/core/security/security_context.h

src/core/security/server_auth_filter.c

src/core/surface/call.c

src/core/transport/transport.h

...2end/tests/request_response_with_payload_and_call_creds.c

test/core/security/auth_context_test.c