First, proxies are certainly not one of the necessary principles of REST. Even without proxies, there can be REST. More importantly, most REST APIs can't take advantage of proxies anyway, because most responses must not be cached.

Second, HTTPS is MITMed using self-signed certificates (signed by custom CAs which are installed in browsers on the network) by proxies all the time. This is very common in corporate networks. Therefore, HTTPS currently works with proxies.