Allow short lived bearer tokens to be used (first implementation being against IBM cloud)

[davidradl]

It would be great for us to be able to use https://ibm.github.io/java-sdk-core/docs/9.17.3/com/ibm/cloud/sdk/core/security/IamAuthenticator.html which handles token refresh for the IBM cloud.

This authenticator is Apache 2 licensed, so could go into this repository. I am thinking that there would be a factory for the authenticator, which would expose an interface allowing the authenticator to be identified and configured and methods exposed to get the latest access token ( under the covers calling https://ibm.github.io/java-sdk-core/docs/9.17.3/com/ibm/cloud/sdk/core/security/IamAuthenticator.html#requestToken--. In the future if other implementations are required then they could be added to the factory with a new identifier.

[kristoffSC]

This sounds very good, Looking forward to see it done :) THX!