Allow SSO for CA admin via LTI

[emmachughes]

This brings back single sign-on for CA's admin, via LTI.

To access admin via SSO:

1. Be an administrator in the hub
2. Add a tool with https://ca.edlib.test/lti/admin as the launch URL, and CA's key/secret
3. Launch the tool

[codecov]

Codecov Report

Merging #2682 (7963115) into master (f31eefb) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2682      +/-   ##
============================================
- Coverage     69.59%   69.57%   -0.02%     
- Complexity     2704     2705       +1     
============================================
  Files           272      272              
  Lines         11997    12000       +3     
============================================
  Hits           8349     8349              
- Misses         3648     3651       +3     

Components	Coverage Δ
contentauthor	69.57% <0.00%> (-0.02%)	⬇️