Is this way to check API security right?

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C#

WCF

jQuery

I have rest Api which I used internally and also used by third party.My question is:I use oauth authentication in this when api called from third party I use to check signature but now i have to allow my internal application call without checking the oauth authentication because to reduce overhead.So I planned get a IP address from where my API called and on that basis I decide oauth authentication required or not.But I have to know my own android application call this Api so in that case IP track possible and ya this whole technique is good or it have drawbacks...My Api is in c#. Thanks in advance