server: add error HTML templates with error description.

server/templates.go

@@ -17,6 +17,7 @@ const (
 	tmplLogin    = "login.html"
 	tmplPassword = "password.html"
 	tmplOOB      = "oob.html"
+	tmplError    = "error.html"
 )
 
 var requiredTmpls = []string{
@@ -24,6 +25,7 @@ var requiredTmpls = []string{
 	tmplLogin,
 	tmplPassword,
 	tmplOOB,
+	tmplError,
 }
 
 type templates struct {
@@ -31,6 +33,7 @@ type templates struct {
 	approvalTmpl *template.Template
 	passwordTmpl *template.Template
 	oobTmpl      *template.Template
+	errorTmpl    *template.Template
 }
 
 type webConfig struct {
@@ -156,6 +159,7 @@ func loadTemplates(c webConfig, templatesDir string) (*templates, error) {
 		approvalTmpl: tmpls.Lookup(tmplApproval),
 		passwordTmpl: tmpls.Lookup(tmplPassword),
 		oobTmpl:      tmpls.Lookup(tmplOOB),
+		errorTmpl:    tmpls.Lookup(tmplError),
 	}, nil
 }
 
@@ -222,6 +226,14 @@ func (t *templates) oob(w http.ResponseWriter, code string) error {
 	return renderTemplate(w, t.oobTmpl, data)
 }
 
+func (t *templates) err(w http.ResponseWriter, errType string, errMsg string) error {
+	data := struct {
+		ErrType string
+		ErrMsg  string
+	}{errType, errMsg}
+	return renderTemplate(w, t.errorTmpl, data)
+}
+
 // small io.Writer utility to determine if executing the template wrote to the underlying response writer.
 type writeRecorder struct {
 	wrote bool