public static StubTransformer fixedCredentialsStubTransformer(final CallCredentials credentials) {
        requireNonNull(credentials, "credentials");
        return (name, stub) -> stub.withCallCredentials(credentials);
    }
Creates a new {@link StubTransformer} that will assign the given credentials to the given {@link AbstractStub}.

@param credentials The call credentials to assign.
@return The transformed stub.
@see AbstractStub#withCallCredentials(CallCredentials)
grpc-client-spring-boot-starter/src/main/java/net/devh/boot/grpc/client/security/CallCredentialsHelper.java