Fix documentation for auth_request directive
Fix documentation for auth_request directive

The correct endpoint is /oauth2/auth
tamsky/oauth2_proxy,coreos/oauth2_proxy,18F/oauth2_proxy,kalibrr/oauth2_proxy,ITNG/oauth2_proxy,jehiah/oauth2_proxy,andyuc88/oauth2_proxy_azure,ITNG/oauth2_proxy,snormore/oauth2_proxy,tamsky/oauth2_proxy,18F/oauth2_proxy,bitly/oauth2_proxy,bitly/google_auth_proxy,ploxiln/oauth2_proxy,Shopify/google_auth_proxy,Shopify/google_auth_proxy,Shopify/google_auth_proxy,bitly/oauth2_proxy,coreos/oauth2_proxy,ploxiln/oauth2_proxy,kbudde/oauth2_proxy,kalibrr/oauth2_proxy,jehiah/oauth2_proxy,andyuc88/oauth2_proxy_azure,snormore/oauth2_proxy,bitly/google_auth_proxy,kbudde/oauth2_proxy