LDAP plugin

[DanielAuerX]

Hi, just wanted to check if there is interest in a ldap plugin such as this.

Obviously, some things that are specific to my use case have to be changed before merged, such as the login html and the email dummy solution.

included in this pr:

• authentication via ldap
• authentication via ldaps
• mount and set cert for private ca
• user attribute can be set to support both openldap vs active directory (uid vs samaccountname)

some ideas for future improvement:

• better handling of failed logins
• better solution for the login page (?)

[LinkinStars]

@DanielAuerX Thank you very much for your contribution. A related issue has been mentioned before. #19 #61
You don't have to worry about the front-end UI. When you finish the feature, we will help to improve it.

[DanielAuerX]

Hi @LinkinStars, currently i see two issues:

1. login page: since one is not redirected to separately hosted login page (e.g. the case with the google connector), i am uising the ResponseWriter (wrapped in the GinContext) to provide the user with the login page. I used css specific to my use case, so currently its a plain html login page. Either we could add some default css, let the user upload his/her own css or maybe you have a completely different solution?
2. since i did not want to send user credentials with a get request, i added an additional endpoint in my implementation added to the answer core. Namely a post endpoint to the PluginAPIRouter calling ConnectorController.ConnectorRedirectDispatcher