Redmine

Dear all,

I am trying to find a solution to authenticate Redmine users against an external Web Service using SOAP.
I think I need to write a subclass of AuthSource, but I don't know how I should do this for a Web Service specifically. I have read the Alternativecustom_authentication_HowTo page, but I don't know how to apply this for Web Services.
Could you please give me a direction where to look? Or is there a plugin already available for this?

Best regards,
Koen