I have integrated paypal mobile checkout library in my iOS application and I am able to do transaction in sandbox environment but I want first seller/merchant to login to my application using paypal access like the images below.

I have referred many links for the same .But not getting any idea.
Please help me .
Thanks in advance.
Here are some links:
https://www.x.com/developers/paypal/documentation-tools/getting-to-know-paypal-access
https://www.x.com/developers/paypal/documentation-tools/api
http://answers.oreilly.com/topic/2528-how-to-use-paypals-mobile-express-checkout-library-for-ios/
There is “GetVerifiedStatus” api provided by paypal which is used to check whether user is having correct paypal email address .I have solved it using the link below:
https://www.x.com/developers/paypal/documentation-tools/api/getverifiedstatus-api-operation