This can be done using the LimitReqModule with Nginx. However if this is for a reverse proxy you might want to try out the new rate limiting supported by HAProxy.

I found the nginx rate limiting to be a little bit confusing to get the exact rate you want.

But you basically have something like:

limit_req_zone $binary_remote_addr zone=default:10m rate=50r/m;

in the http section and then something like the following in the location section within the server section:

limit_req zone=default burst=10 nodelay;