Implement Shibboleth

[SamuelWei]

Fixes #20

Type (Highlight the corresponding type)

• Bugfix
• Feature
• Documentation
• Refactoring (e.g. Style updates, Test implementation, etc.)
• Other (please describe):

Checklist

• Code updated to current masters head
• Passes CI checks
• Is a part of an issue
• Tests added for the bugfix or newly implemented feature, describe below why if not
• Changelog is updated
• Documentation of code and features exists

Changes

• Implement Shibboleth with apache mod _shib
• Adjust Greenlight v2 migration script to impot social users from Greenlight v2
• Add database transactions to Greenlight v2 migration script to revert changes on errors
• Fix error on Greenlight v2 migration, room feature 'Room Authentication' missing
• Fix error on Greenlight v2 migration, room name too long (truncate room name after max. lenght)

[accesslint]

There are accessibility issues in these changes.

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (39ddfca) 94.76% compared to head (9cee464) 94.70%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #497      +/-   ##
============================================
- Coverage     94.76%   94.70%   -0.06%     
- Complexity      962     1007      +45     
============================================
  Files           260      272      +12     
  Lines          6303     6481     +178     
  Branches        521      526       +5     
============================================
+ Hits           5973     6138     +165     
- Misses          315      328      +13     
  Partials         15       15              

Files	Coverage Δ
app/Auth/ExternalUser.php	100.00% <100.00%> (ø)
app/Auth/LDAP/LDAPProvider.php	65.21% <100.00%> (ø)
app/Auth/Shibboleth/ShibbolethController.php	100.00% <100.00%> (ø)
app/Auth/Shibboleth/ShibbolethProvider.php	100.00% <100.00%> (ø)
app/Auth/Shibboleth/ShibbolethServiceProvider.php	100.00% <100.00%> (ø)
...Shibboleth/ShibbolethSessionDuplicateException.php	100.00% <100.00%> (ø)
...pp/Auth/Shibboleth/ShibbolethSessionMiddleware.php	100.00% <100.00%> (ø)
app/Auth/Shibboleth/ShibbolethUser.php	100.00% <100.00%> (ø)
app/Auth/Shibboleth/SoapServerHandler.php	100.00% <100.00%> (ø)
...p/Http/Controllers/api/v1/auth/LoginController.php	100.00% <100.00%> (ø)
... and 14 more

... and 1 file with indirect coverage changes

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