Currently I'm using apigee console to test my API REST resources. the Oauth works great when I login with a "salesforce" licensed user, but if I tried to log in with a portal user it does not let me in. Seems like I'm not setting correctly the URL for authentication. I know portal user must authenticate using the force.com url and not login.salesforce nor test.salesforce URL, so what's the correct URL to do the authentication against?
Here is a fairly new article that describes this and check the comments section also for common mistakes and fixes.
The URL needs to be: