Docs:
MitID Documentation : MitID | Developer Pages
Authentication Documentation: Authentication | Developer Pages
Auth API (OIDC): Authentication API | Developer Pages
Tools:
MitID test tool : MitID Test Tool
Customer Portal login (only for going to prod): https://customerportal.signicat.com/
Sample code : https://github.com/signicat-hackathon
Other:
Information from Digitaliseringsstyrelsens webpages : MitID