Indicates whether this credential requires transport security (TLS).
When true (the default), the credential will only be applied to calls over secure transports. If transport security is not present, the call will fail with kotlinx.rpc.grpc.GrpcStatusCode.UNAUTHENTICATED.
Set to false only for credentials that are safe to send over insecure connections, such as in testing environments or for non-sensitive authentication mechanisms.
Return
true if transport security is required, false otherwise.