Docs:
MitID Documentation : MitID | Developer Pages
Signature Documentation: Electronic signatures | Developer Pages
Sign API (REST): Sign API v1 | 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
Postman example for Sign API: https://www.postman.com/collections/72636ac6bc6b63d184dd
Other:
Information from Digitaliseringsstyrelsens webpages : MitID