Add support for authentication using certificates

[kusha]

client_cert and ca_certs are new parameters of CMRESHandler. CERT_AUTH is an alais for NO_AUTH to support both cert + HTTP auth for other authentication methods.

[codecov-io]

Codecov Report

Merging #55 into master will decrease coverage by 0.5%. The diff coverage is 62.5%.

@@            Coverage Diff            @@
##           master     #55      +/-   ##
=========================================
- Coverage      83%   82.5%   -0.51%     
=========================================
  Files           2       2              
  Lines         153     160       +7     
  Branches       20      21       +1     
=========================================
+ Hits          127     132       +5     
- Misses         22      23       +1     
- Partials        4       5       +1

Impacted Files	Coverage Δ
cmreslogging/handlers.py	81.69% <62.5%> (-0.5%)	:arrow_down:

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