Support rewriting status codes in error page middleware

integration/error_pages_test.go

@@ -69,6 +69,30 @@ func (s *ErrorPagesSuite) TestErrorPage() {
 	require.NoError(s.T(), err)
 }
 
+func (s *ErrorPagesSuite) TestStatusRewrites() {
+	// The `statusRewrites.toml` file contains a misconfigured backend host and some status code rewrites.
+	file := s.adaptFile("fixtures/error_pages/statusRewrites.toml", struct {
+		Server1 string
+		Server2 string
+	}{s.BackendIP, s.ErrorPageIP})
+
+	s.traefikCmd(withConfigFile(file))
+
+	frontendReq, err := http.NewRequest(http.MethodGet, "http://127.0.0.1:8080", nil)
+	require.NoError(s.T(), err)
+	frontendReq.Host = "test502.local"
+
+	err = try.Request(frontendReq, 2*time.Second, try.BodyContains("An error occurred."), try.StatusCodeIs(404))
+	require.NoError(s.T(), err)
+
+	frontendReq, err = http.NewRequest(http.MethodGet, "http://127.0.0.1:8080", nil)
+	require.NoError(s.T(), err)
+	frontendReq.Host = "test418.local"
+
+	err = try.Request(frontendReq, 2*time.Second, try.BodyContains("An error occurred."), try.StatusCodeIs(400))
+	require.NoError(s.T(), err)
+}
+
 func (s *ErrorPagesSuite) TestErrorPageFlush() {
 	srv := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 		rw.Header().Add("Transfer-Encoding", "chunked")

integration/fixtures/error_pages/statusRewrites.toml

@@ -0,0 +1,45 @@
+[global]
+  checkNewVersion = false
+  sendAnonymousUsage = false
+
+[log]
+  level = "DEBUG"
+  noColor = true
+
+[entryPoints]
+  [entryPoints.web]
+    address = ":8080"
+
+[providers.file]
+  filename = "{{ .SelfFilename }}"
+
+## dynamic configuration ##
+
+[http.routers]
+  [http.routers.router1]
+    rule = "Host(`test502.local`)"
+    service = "service1"
+    middlewares = ["error"]
+  [http.routers.router2]
+    rule = "Host(`test418.local`)"
+    service = "noop@internal"
+    middlewares = ["error"]
+
+[http.middlewares]
+  [http.middlewares.error.errors]
+    status = ["500-502", "503-599", "418"]
+    service = "error"
+    query = "/50x.html"
+    [http.middlewares.error.errors.statusRewrites]
+      "418" = 400
+      "500-502" = 404
+
+[http.services]
+  [http.services.service1.loadBalancer]
+    passHostHeader = true
+    [[http.services.service1.loadBalancer.servers]]
+      url = "http://{{.Server1}}:8989474"
+
+  [http.services.error.loadBalancer]
+    [[http.services.error.loadBalancer.servers]]
+      url = "http://{{.Server2}}:80"

integration/fixtures/k8s/01-traefik-crd.yml

@@ -1003,6 +1003,8 @@ spec:
                     description: |-
                       Query defines the URL for the error page (hosted by service).
                       The {status} variable can be used in order to insert the status code in the URL.
+                      The {originalStatus} variable can be used in order to insert the upstream status code in the URL.
+                      The {url} variable can be used in order to insert the escaped request URL.
                     type: string
                   service:
                     description: |-
@@ -1199,6 +1201,13 @@ spec:
                     items:
                       type: string
                     type: array
+                  statusRewrites:
+                    additionalProperties:
+                      type: integer
+                    description: |-
+                      StatusRewrites defines a mapping of status codes that should be returned instead of the original error status codes.
+                      For example: "418": 404 or "410-418": 404
+                    type: object
                 type: object
               forwardAuth:
                 description: |-