Classlink Auth Support

[Jaqster]

Classlink is an educational federated authentication provider (like Clever). We've had a few different customers asking us for Classlink auth support. Opening this issue to investigate the level of effort to support. Docs:

• https://help.classlink.com/s/article/pp-cl-oneclick
• https://help.classlink.com/s/article/OAuth2-Workflow
• https://help.classlink.com/s/article/Requesting-Authorization-for-Access
• https://help.classlink.com/s/article/Obtaining-Bearer-Tokens
• https://help.classlink.com/s/article/pp-access-user-data
• https://help.classlink.com/s/article/Handling-Unknown-Users