Add support for CAS auth strategy

[chownces]

Description

Opening a draft PR for CAS authentication to support the teaching team at UU in the interim. Currently, the frontend only supports the OAuth2 specification.

Im planning to do a proper follow up sometime in Dec '22 before merging this. Or whoever is interested in taking this up, please feel free to let me know too 🙂:

• proper handling of the URL parameters depending on which auth provider type is being used
• add test cases

Corresponding backend PR: source-academy/backend#916

Type of change

• New feature (non-breaking change which adds functionality)

How to test

TBC

Checklist

• I have tested this code
• I have updated the documentation

[coveralls]

Pull Request Test Coverage Report for Build 3354297238

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 9 of 17 (52.94%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 32.964%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/commons/utils/Constants.ts	6	9	66.67%
src/commons/utils/AuthHelper.ts	0	5	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/commons/utils/AuthHelper.ts	1	34.09%

Totals
Change from base Build 3255802840:	0.004%
Covered Lines:	4330
Relevant Lines:	12219

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💛 - Coveralls

[RichDom2185]

Can I check what's left for this PR?

[RichDom2185]

As per discussed offline, this PR is ready and simply blocked by awaiting the tests to be implemented in the corresponding backend PR: source-academy/backend#916.

[RichDom2185]

I think I'll merge this first because we'll need some of the refactoring work you've done to implement SAML.

Thanks!