Any experience with Mutual Authentication and OAuth 2.0?

One of the web services I have used in the past is revising their APIs and implementing Mutual Authentication or OAuth 2.0. I need to understand what I need to do to make this change from basic Bearer Token authentication. If anyone has skills implementing either you wouldn’t mind sharing, that would be great. Thanks in advance for your replies!.. Don

for alexa, account linking supports OAuth2

old tutorial is here.