Add JWT and login support

[MichaelJCompton]

Not sure of the current status of this. Some of the commits are old, but look reasonable.

I think we should:

• make these commits - potentially with some refactoring and making sure the testing is all in place
• merge the other two pending pull requests
• do any package and dependency updates that are required
• add the Slash GraphQL token support
• any updates needed for 20.11.0
• after all those ^^ release a new version as 20.11.0

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