How to map the target endpoint URL parameters to the proxy url

[arunk]

I have a target endpoint in the below format. How do I map these target endpoint URL parameters to the proxy URL params. As the mobile parameter can change based on the request from user. How to account for this change and dynamically configure the proxy URL and target URL.

http://control.msg91.com/api/sendotp.php?template=&otp_length=&authkey=&message=&sender=&mobile=&otp...