Getting url requested to server

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ASP.NET

i m working on asp.net website.When user logs in website, whatever link he clicks or uploads file we have maintained session ids to check whether user is authenticated to do so.we use global.asax function authenticate to check if user is auhenticated
In Response.Cookies["RSID"].Value ,Request.Cookies["RSID"].Value, we maintain session ids and compare the session id in Request.Cookies["RSID"] with session id stored at server.
When user clicks any link we send sessionid (currently stored in Request.Cookies["RSID"]) to server and at server we check it whether this session id matches with session id stored in server.If match then authenticate user else user is forced out.

We have maintained logs to trace the flow of requests.
Now When user clicks any link, the request containing session ids goes to server.
In logs we are able to track which session ids request is gone to server.
But we want to trace in logs the urls along with session ids requested to server.

In our file upload functionality, when user clicks upload button, one session id request goes to server and in response it gets new session id which is then mapped to Response.Cookies["RSID"].Value ,Request.Cookies["RSID"].Value at website and in a variable a server. After this data in file is inserted in database.

From last some days when upload file button is clicked, as flow session id requesy goes to server , new session id is mapped to variables at server and website and when some records are inserted in databse again the session id request (which was gone to server on upload button click) goes to server.But now since new session id is mappd to session id variable at server, session id mismatch occurs and user is forcd out.This behaviour is occuring suddenly although no code changes where done.

This behavior is not replicated when debug through code or when website is hosted on our testing iis.
While uploading we are not clicking upload again again then too the session id request is going to server.
We came to know this through logs written in program.

From session ids we are not getting actually for what url or functionality request i going to server.
i read about event logs,logging and tracing, health monitoring but not getting actually how to get the url which is requested to server.

Can someone tell me how to get this requested url.