Toniof 1191 add cryptography

[TonioF]

Fixes #1191 . The issue was that the cryptography package is declared an optional dependency of pyjwt (which is a required xcube package) and a required dependency of moto (which is a dev only dependency of xcube). In consequence, all xcube developers had this package installed and did not stumble across this issue.
I added cryptography as xcube dependency, because apparently so far we relied in the code on its presence. However, I also removed the explicit call of a specific algorithm from xcubeto prevent such situations. If I see it correctly, the code would also work with other (i.e., non-RSA) algorithms, but I did not test this.

Checklist:

* [ ] Add unit tests and/or doctests in docstrings
* [ ] Add docstrings and API docs for any new/modified user-facing classes and functions
* [ ] New/modified features documented in docs/source/*

• Changes documented in CHANGES.md
• GitHub CI passes
• AppVeyor CI passes
• Test coverage remains or increases (target 100%)

[pont-us]

Looks good! I just added some comments and additional version restrictions as suggestions. I haven't tested with non-RSA algorithms either, but evidently this was not needed so far anyway. Either way, get_algorithm_by_name seems like a cleaner way to implement the current functionality.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.54%. Comparing base (3e65d5d) to head (3f6f313).

Files with missing lines	Patch %	Lines
xcube/webapi/auth/context.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1199      +/-   ##
==========================================
- Coverage   89.55%   89.54%   -0.01%     
==========================================
  Files         280      280              
  Lines       21653    21655       +2     
==========================================
  Hits        19391    19391              
- Misses       2262     2264       +2     

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[clarasb]

Thanks @TonioF! Looks good to me.

[forman]

Good, thanks! Please apply @pont-us' suggestions.