Allow specify header in ServerBearerTokenAuthenticationConverter

[TJReinert]

Summary

I'd like to be able to use the current ServerBearerTokenAuthenticationConverter but want to use a different header (HttpHeaders.PROXY_AUTHORIZATION) for my Spring Cloud Gateway Instance.

Actual Behavior

Authentication must be taken from the HttpHeaders.AUTHORIZATION.

Expected Behavior

I should be able to supply what Header I would like to extract my token from. If not specified default to HttpHeaders.AUTHORIZATION.

Version

All versions, enhancement request.

Notes

These changes are straight forward and I can open a PR for these changes if deemed necessary.

[jzheaux]

That makes sense, @TJReinert, would you be interested in submitting a PR to add that feature?

[TJReinert]

Sure thing. Please coach me if there are improvements desired -- first submission to an opensource project.