Adds configuration for OAuth library's authentication style.

internal/configuration/config.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"golang.org/x/oauth2"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -30,6 +31,7 @@ var (
 
 // Config holds app configuration
 type Config struct {
+	AuthStyle string `long:"auth-style" env:"AUTH_STYLE" default:"auto-detect" choice:"auto-detect" choice:"header" choice:"params" description:"Optionally choose the authentication style of the OAuth2 library."`
 	LogLevel  string `long:"log-level" env:"LOG_LEVEL" default:"warn" choice:"trace" choice:"debug" choice:"info" choice:"warn" choice:"error" choice:"fatal" choice:"panic" description:"Log level"`
 	LogFormat string `long:"log-format"  env:"LOG_FORMAT" default:"text" choice:"text" choice:"json" choice:"pretty" description:"Log format"`
 
@@ -133,6 +135,17 @@ func (c *Config) parseFlags(args []string) error {
 	return nil
 }
 
+func (c *Config) ParseAuthStyle() oauth2.AuthStyle {
+	switch c.AuthStyle {
+	case "header":
+		return oauth2.AuthStyleInHeader
+	case "params":
+		return oauth2.AuthStyleInParams
+	default:
+		return oauth2.AuthStyleAutoDetect
+	}
+}
+
 func (c *Config) parseUnknownFlag(option string, arg flags.SplitArgument, args []string) ([]string, error) {
 	// Parse rules in the format "rule.<name>.<param>"
 	parts := strings.Split(option, ".")

internal/configuration/config_test.go

@@ -1,6 +1,7 @@
 package configuration
 
 import (
+	"golang.org/x/oauth2"
 	"os"
 	"testing"
 	"time"
@@ -23,6 +24,7 @@ func TestConfigDefaults(t *testing.T) {
 	assert.Equal("text", c.LogFormat)
 
 	assert.Equal("", c.AuthHost)
+	assert.Equal("auto-detect", c.AuthStyle)
 	assert.Len(c.CookieDomains, 0)
 	assert.False(c.InsecureCookie)
 	assert.Equal("_forward_auth", c.CookieName)
@@ -37,6 +39,7 @@ func TestConfigDefaults(t *testing.T) {
 func TestConfigParseArgs(t *testing.T) {
 	assert := assert.New(t)
 	c, err := NewConfig([]string{
+		"--auth-style=header",
 		"--cookie-name=cookiename",
 		"--csrf-cookie-name", "\"csrfcookiename\"",
 		"--rule.1.action=allow",
@@ -47,6 +50,7 @@ func TestConfigParseArgs(t *testing.T) {
 	require.Nil(t, err)
 
 	// Check normal flags
+	assert.Equal("header", c.AuthStyle)
 	assert.Equal("cookiename", c.CookieName)
 	assert.Equal("csrfcookiename", c.CSRFCookieName)
 
@@ -118,6 +122,24 @@ func TestConfigParseIni(t *testing.T) {
 	}, c.Rules)
 }
 
+func TestConfigParseAuthStyle(t *testing.T) {
+	assert := assert.New(t)
+
+	c1, err := NewConfig([]string{})
+	assert.Nil(err)
+	assert.Equal(oauth2.AuthStyleAutoDetect, c1.ParseAuthStyle())
+
+	c2, err := NewConfig([]string{})
+	c2.AuthStyle = "params"
+	assert.Nil(err)
+	assert.Equal(oauth2.AuthStyleInParams, c2.ParseAuthStyle())
+
+	c3, err := NewConfig([]string{})
+	c3.AuthStyle = "header"
+	assert.Nil(err)
+	assert.Equal(oauth2.AuthStyleInHeader, c3.ParseAuthStyle())
+}
+
 func TestConfigParseEnvironment(t *testing.T) {
 	assert := assert.New(t)
 	os.Setenv("COOKIE_NAME", "env_cookie_name")

internal/handlers/server.go

@@ -290,12 +290,17 @@ func (s *Server) AuthCallbackHandler() http.HandlerFunc {
 			scope = []string{oidc.ScopeOpenID, "profile", "email", "groups"}
 		}
 
+		endpoint := provider.Endpoint()
 		oauth2Config := oauth2.Config{
 			ClientID:     s.config.ClientID,
 			ClientSecret: s.config.ClientSecret,
 			RedirectURL:  s.authenticator.ComposeRedirectURI(r),
-			Endpoint:     provider.Endpoint(),
-			Scopes:       scope,
+			Endpoint: oauth2.Endpoint{
+				AuthStyle: s.config.ParseAuthStyle(),
+				AuthURL:   endpoint.AuthURL,
+				TokenURL:  endpoint.TokenURL,
+			},
+			Scopes: scope,
 		}
 
 		// Exchange code for token