More robust endpoint URL parsing

auth.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 
 	"golang.org/x/crypto/ssh"
 )
@@ -52,23 +53,28 @@ type Authenticator interface {
 	Auth(request AuthRequest, username string) (int, *AuthResponse, error)
 }
 
-func makeAuthenticator(auth AuthConfig) Authenticator {
+func makeAuthenticator(auth AuthConfig) (Authenticator, error) {
 	if auth.Version == "" {
 		auth.Version = "v1"
 	}
 	headers := http.Header{}
 	for _, header := range auth.Headers {
 		headers.Add(header.Name, header.Value)
 	}
-	return &RESTfulAuthenticator{
-		Endpoint: auth.Endpoint,
+	auth_url, err := url.Parse(auth.Endpoint)
+	if err != nil {
+		return nil, err
+	}
+	authenticator := RESTfulAuthenticator{
+		Endpoint: auth_url,
 		Version:  auth.Version,
 		Headers:  headers,
 	}
+	return &authenticator, nil
 }
 
 type RESTfulAuthenticator struct {
-	Endpoint string
+	Endpoint *url.URL
 	Version  string
 	Headers  http.Header
 }
@@ -77,16 +83,19 @@ func (auth *RESTfulAuthenticator) Auth(request AuthRequest, username string) (in
 	if auth.Version != "v1" {
 		return 500, nil, fmt.Errorf("unsupported API version: %s", auth.Version)
 	}
-	url := fmt.Sprintf("%s/v1/auth/%s", auth.Endpoint, username)
+	auth_url := auth.Endpoint.JoinPath("v1", "auth", username).String()
+
 	payload := new(bytes.Buffer)
 	if err := json.NewEncoder(payload).Encode(request); err != nil {
 		return 0, nil, err
 	}
-	req, err := http.NewRequest("POST", url, payload)
+
+	req, err := http.NewRequest("POST", auth_url, payload)
 	if err != nil {
 		return 0, nil, err
 	}
 	req.Header = auth.Headers
+
 	res, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return res.StatusCode, nil, err
@@ -96,6 +105,7 @@ func (auth *RESTfulAuthenticator) Auth(request AuthRequest, username string) (in
 	if err != nil {
 		return res.StatusCode, nil, err
 	}
+
 	var response AuthResponse
 	err = json.Unmarshal(body, &response)
 	if err != nil {

sshmux.go

@@ -106,7 +106,11 @@ func makeServer(config Config) (*Server, error) {
 		legacyAuthenticator := makeLegacyAuthenticator(config.Auth, config.Recovery)
 		authenticator = &legacyAuthenticator
 	} else {
-		authenticator = makeAuthenticator(config.Auth)
+		var err error
+		authenticator, err = makeAuthenticator(config.Auth)
+		if err != nil {
+			return nil, err
+		}
 	}
 	sshmux := &Server{
 		Address:       config.Address,