Add optional Openid connect provider issuer url to config and update passport.js to use it

[rcrichton]

This pull request adds the ability to specify an optional Openid connect provider issuer url in the config file. If provided, passport.js will use this url instead of the api url. This change ensures that the correct issuer url is used when using a proxy.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3b9a686) 86.76% compared to head (c5f8cbb) 86.76%.

❗ Current head c5f8cbb differs from pull request most recent head 0e6267b. Consider uploading reports for the commit 0e6267b to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1215   +/-   ##
=======================================
  Coverage   86.76%   86.76%           
=======================================
  Files          89       89           
  Lines        6024     6024           
=======================================
  Hits         5227     5227           
  Misses        797      797           

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