Best way to differentiate between browser requests and requests from mobile apps?

I have some actions in my app that require a user to have logged in on the website, and some that require a "person" (a mobile app user basically) to have authenticated. In order to know whether i need to push the current request through the mobile authentication, i'd like to be able to tell whether the request came from a browser or fr开发者_StackOverflow中文版om an iphone for example.

Is there a request header or something i can look at for this?

thanks, max

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take a look at mobile_fu