Rewrite Help

Hi. I'm configuring nginx as reverse proxy.

I need to change (rewrite?) the URLs, example: if the request (to nginx Reverse Proxy) is "http://domain.com/test/?username=test1;password=passwdtest1" it will must "modified" to the main server as "http://domain.com/test/?username=production;password=passwdproduction1".

Consider that in the original request the fields "username=test1;password=passwdtest1" are not always the same (they changes), instead the "modified" to the main server are always the same.

Others example to be more clear:

"http://domain.com/test/?username=test1;password=passwdtest1" -> "http://domain.com/test/?username=production;password=passwdproduction1"

"http://domain.com/test/?username=test1876;password=somepasswd" -> "http://domain.com/test/?username=production;password=passwdproduction1"

"http://domain.com/test/?username=somevalues;password=somepasswdvalue" -> "http://domain.com/test/?username=production;password=passwdproduction1"


Thanks!