Security notice

• The state parameter is a critical part of the OAuth2 handshake, used to prevent CSRF attacks. The Edx, AngelList and Questrade providers were originally added without state support, as these providers did not support it at the time. Edx and Questrade have since added support, so their configuration has been updated accordingly. AngelList is no longer operational and has been removed. Thanks to Adil Ahmadzada for reporting.