Remove ReverseProxy authentication from the API

Since we changed the /api/v1/ routes to disallow session authentication we also
removed their reliance on CSRF. However, we left the ReverseProxy authentication
here - but this means that POSTs to the API are no longer protected by CSRF.

Now, ReverseProxy authentication is a kind of session authentication, and is
therefore inconsistent with the removal of session from the API.

This PR proposes that we simply remove the ReverseProxy authentication from the
API and therefore users of the API must explicitly use tokens or basic authentication.

Replace go-gitea#22077

Signed-off-by: Andrew Thornton <art27@cantab.net>

routers/api/v1/api.go

@@ -232,9 +232,6 @@ func reqExploreSignIn() func(ctx *context.APIContext) {
 
 func reqBasicOrRevProxyAuth() func(ctx *context.APIContext) {
 	return func(ctx *context.APIContext) {
-		if ctx.IsSigned && setting.Service.EnableReverseProxyAuth && ctx.Data["AuthedMethod"].(string) == auth.ReverseProxyMethodName {
-			return
-		}
 		if !ctx.Context.IsBasicAuth {
 			ctx.Error(http.StatusUnauthorized, "reqBasicOrRevProxyAuth", "auth required")
 			return
@@ -598,9 +595,6 @@ func buildAuthGroup() *auth.Group {
 		&auth.HTTPSign{},
 		&auth.Basic{}, // FIXME: this should be removed once we don't allow basic auth in API
 	)
-	if setting.Service.EnableReverseProxyAuth {
-		group.Add(&auth.ReverseProxy{})
-	}
 	specialAdd(group)
 
 	return group