wild card match on request headers for nginx

I am using nginx as a proxy server to send the requests to backend pool members .

I have a header -- Content-Type: multipart/form-data; boundary="21ad608c-8e00-4c0c-8a06-5ed1280e9532" The boundary value in the header changes all the time.

How can I do a header check for only "Content-Type: multipart/form-data;" value and route the requests to the backend. when I do a print of $http_content_type value , everything including boundary value is getting printed . I am not able to do an if check on just " Content-Type: multipart/form-data; " value .

Can I put a wild card in the nginx config like -- "multipart/form-data; * " to pass the if loop ?

Please let me know.