Idea: Attempt to authenticate tokens without X-Token-Type

[djones6]

The Credentials plugins require an X-Token-Type header to be set to one of JWT, GoogleToken, or FacebookToken in order to determine which plugin should attempt to handle a request.

However, a potential use-case is that Credentials is used solely with JWT authentication, and with a 3rd party client that supplies the standard Authorization: Bearer <token> header. In this scenario, the X-Token-Type: JWT header would need to be manually set in order to work with Credentials.

In addition, when constructing usage examples where the curl command-line is used, the extra header is a distraction:

curl -H 'Authorization: Bearer <token>' -H 'X-token-type: JWT' http://localhost:8080/protectedRoute

We could relax the requirements for authentication so that Credentials plugins attempt to authenticate a request if the X-Token-Type header is not set.