First of all, putting the credentials in the URL would be insecure.
The best way to accomplish what you're trying to do would be to use OpenID Connect, which was designed to support mobile (i.e. non-web) applications where you can't redirect the person.
In the [authentication request](http://openid.net/specs/openid-connect-core-1_0.html#AuthRequest) you can set "prompt=none" and "fulfill other conditions for processing" by sending the credentials.
Some more links on OpenID Connect to consider.
- [Slides ](http://wiki.openid.net/w/file/fetch/80030063/OpenID_Connect_Overview_May_5_2014.pdf)from Mike Jones, Microsoft:
- [Great overview](http://gluu.co/connect-deep-dive) from Travis Spencer (former ping CTO)t
- Short [overview ](http://gluu.co/oauth2-v-openid-connect)on OAuth2 v. OpenID Connect
- Minimalist [blog](http://nat.sakimura.org/2012/03/31/openid-connect-stripped-down-to-just-authentication) from Nat Sakimura