Creating your own authentication mechanism involves a lot of work and exposes your system to attacks due to breaches you are not aware of or did not handle correctly.
On the other hand, there are 3rd-party vendors which have very solid, tested and trust-worthy authentication mechanisms you can use to you own application benefit, such as Google, Github, etc.
This micro-service aims to help you integrate with those 3rd-party authenticators.
Once set up and triggered this micro-service initiates an authentication flow which validates the user against the 3rd-party authentication vendor, and if valid, returns the user's approved details to be shared with your application.
Every respectable authentication vendor has means to preform authentication. This micro-service simply consolidates the different vendors and exposes an abstraction API to work with them.
Here it is: https://github.com/mbarzeev/third-auth-ms