Add auth_key for session classes

[Zapix]

closes #129

[codecov]

Codecov Report

Merging #134 (cdaa7b6) into dev (e16041f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #134   +/-   ##
=======================================
  Coverage   99.32%   99.32%           
=======================================
  Files         197      197           
  Lines        5602     5628   +26     
=======================================
+ Hits         5564     5590   +26     
  Misses         38       38           

Flag	Coverage Δ
unittests	99.32% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
mtpylon/middlewares/set_session_id.py	100.00% <100.00%> (ø)
mtpylon/sessions/in_memory_session_storage.py	100.00% <100.00%> (ø)
mtpylon/sessions/session_event.py	100.00% <100.00%> (ø)
mtpylon/sessions/session_storage_protocol.py	100.00% <100.00%> (ø)
mtpylon/sessions/session_subject.py	100.00% <100.00%> (ø)
tests/test_middlewares/test_session_id.py	100.00% <100.00%> (ø)
...ts/test_sessions/test_in_memory_session_storage.py	100.00% <100.00%> (ø)
tests/test_sessions/test_session_subject.py	100.00% <100.00%> (ø)

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