Fix Properly join configuration URLs

[eburkland]

A Change was made in 3.4.0.0 commit (0a49eb5) which creates an improper "well-known" URL. Change it back please

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[codecov]

Codecov Report

Merging #588 (6330b3f) into master (ca68410) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #588   +/-   ##
=======================================
  Coverage   76.11%   76.11%           
=======================================
  Files         314      314           
  Lines        9471     9471           
  Branches      464      464           
=======================================
  Hits         7209     7209           
  Misses       2110     2110           
  Partials      152      152           

Flag	Coverage Δ
unittests	76.11% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
social_core/backends/okta.py	92.30% <ø> (ø)

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[nijel]

Merged, thanks for your contribution!