Support reverse proxy providing email (#5554)

This PR implements #2347

modules/auth/auth.go

@@ -105,9 +105,16 @@ func SignedInUser(ctx *macaron.Context, sess session.Store) (*models.User, bool)
 
 				// Check if enabled auto-registration.
 				if setting.Service.EnableReverseProxyAutoRegister {
+					email := gouuid.NewV4().String() + "@localhost"
+					if setting.Service.EnableReverseProxyEmail {
+						webAuthEmail := ctx.Req.Header.Get(setting.ReverseProxyAuthEmail)
+						if len(webAuthEmail) > 0 {
+							email = webAuthEmail
+						}
+					}
 					u := &models.User{
 						Name:     webAuthUser,
-						Email:    gouuid.NewV4().String() + "@localhost",
+						Email:    email,
 						Passwd:   webAuthUser,
 						IsActive: true,
 					}