Do not add blank Bearer token

[martinoneutrino]

Request for BearerAuthenticationProvider not to add a blank token to the Authorization header, as doing so will never satisfy any real authorization requirement, and may cause a request failure when multiple Authorization headers are sent due to multiple (optional) security schemes are defined on an endpoint.

This change could be extended to the other AuthProviders, but I have not been using those.

Fixes: #589

[hbelmiro]

@all-contributors add @martinoneutrino to code.

[allcontributors[bot]]

@hbelmiro

I've put up a pull request to add @martinoneutrino! :tada: