Condition in location for proxy_pass

[trm asn]

Dear List ,

I need to do a conditional proxy_pass , but it's not happening as expected
.

like

set $target
http://www.example.com/sso/url.ping?TargetUrl=http://www.example.com/home

And that $target , I would like to check with $request_uri in below segment
.

location /sso/ {
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header Host $http_host;
                proxy_redirect off;
            ----------

            ----------
                proxy_pass         http://10.20.137.21;
                }
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