Move Error page rendering to app package

pkg/app/error_page.go

@@ -0,0 +1,56 @@
+package app
+
+import (
+	"html/template"
+	"net/http"
+
+	"github.com/oauth2-proxy/oauth2-proxy/v7/pkg/logger"
+)
+
+// ErrorPage is used to render error pages.
+type ErrorPage struct {
+	// Template is the error page HTML template.
+	Template *template.Template
+
+	// ProxyPrefix is the prefix under which OAuth2 Proxy pages are served.
+	ProxyPrefix string
+
+	// Footer is the footer to be displayed at the bottom of the page.
+	// If not set, a default footer will be used.
+	Footer string
+
+	// Version is the OAuth2 Proxy version to be used in the default footer.
+	Version string
+}
+
+// Render writes an error page to the given response writer.
+// It uses the passed redirectURL to give users the option to go back to where
+// they originally came from or try signing in again.
+func (e *ErrorPage) Render(rw http.ResponseWriter, status int, redirectURL string, appError string) {
+	rw.WriteHeader(status)
+
+	// We allow unescaped template.HTML since it is user configured options
+	/* #nosec G203 */
+	data := struct {
+		Title       string
+		Message     string
+		ProxyPrefix string
+		StatusCode  int
+		Redirect    string
+		Footer      template.HTML
+		Version     string
+	}{
+		Title:       http.StatusText(status),
+		Message:     appError,
+		ProxyPrefix: e.ProxyPrefix,
+		StatusCode:  status,
+		Redirect:    redirectURL,
+		Footer:      template.HTML(e.Footer),
+		Version:     e.Version,
+	}
+
+	if err := e.Template.Execute(rw, data); err != nil {
+		logger.Printf("Error rendering error template: %v", err)
+		http.Error(rw, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+	}
+}

pkg/app/error_page_test.go

@@ -0,0 +1,35 @@
+package app
+
+import (
+	"html/template"
+	"io/ioutil"
+	"net/http/httptest"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Error Page", func() {
+
+	Context("Render", func() {
+		It("Writes the template to the response writer", func() {
+			tmpl, err := template.New("").Parse("{{.Title}} {{.Message}} {{.ProxyPrefix}} {{.StatusCode}} {{.Redirect}} {{.Footer}} {{.Version}}")
+			Expect(err).ToNot(HaveOccurred())
+
+			errorPage := &ErrorPage{
+				Template:    tmpl,
+				ProxyPrefix: "/prefix/",
+				Footer:      "Custom Footer Text",
+				Version:     "v0.0.0-test",
+			}
+
+			recorder := httptest.NewRecorder()
+			errorPage.Render(recorder, 403, "/redirect", "Access Denied")
+
+			body, err := ioutil.ReadAll(recorder.Result().Body)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(string(body)).To(Equal("Forbidden Access Denied /prefix/ 403 /redirect Custom Footer Text v0.0.0-test"))
+		})
+	})
+
+})