There's a password protected Map Server running IIS that I want to access via REST services, but I don't know how to go about doing the authentication. I keep getting the following message:
I thought maybe I'd be prompted for user/pass but that's not happening. I don't believe I can send the user/pass as part of the REST request itself either, so I'm somewhat lost at this point.
If you are trying to access ArcGIS Server based REST services which are secure then you need to use tokens. The way that security is enabled is in ArcGIS Server Manager.
If you simply have a web application (perhaps web ADF or some custom application) that is protected by IIS then you have work to do.
What specifically do you mean when you say that you have "a password protected Map Server running IIS"?