Add support for client basic auth for exchanging access tokens (#6293)

* Add support for client basic auth for exchanging access tokens

* Improve error messages

* Fix tests

2 files changed, 68 insertions, 1 deletions

diff --git a/integrations/oauth_test.go b/integrations/oauth_test.go
index 53b83bb01a..9674146f8b 100644
--- a/integrations/oauth_test.go
+++ b/integrations/oauth_test.go
@@ -136,3 +136,44 @@ func TestAccessTokenExchangeWithInvalidCredentials(t *testing.T) {
 	})
 	MakeRequest(t, req, 400)
 }
+
+func TestAccessTokenExchangeWithBasicAuth(t *testing.T) {
+	prepareTestEnv(t)
+	req := NewRequestWithValues(t, "POST", "/login/oauth/access_token", map[string]string{
+		"grant_type":    "authorization_code",
+		"redirect_uri":  "a",
+		"code":          "authcode",
+		"code_verifier": "N1Zo9-8Rfwhkt68r1r29ty8YwIraXR8eh_1Qwxg7yQXsonBt", // test PKCE additionally
+	})
+	req.Header.Add("Authorization", "Basic ZGE3ZGEzYmEtOWExMy00MTY3LTg1NmYtMzg5OWRlMGIwMTM4OjRNSzhOYTZSNTVzbWRDWTBXdUNDdW1aNmhqUlBuR1k1c2FXVlJISGpKaUE9")
+	resp := MakeRequest(t, req, 200)
+	type response struct {
+		AccessToken  string `json:"access_token"`
+		TokenType    string `json:"token_type"`
+		ExpiresIn    int64  `json:"expires_in"`
+		RefreshToken string `json:"refresh_token"`
+	}
+	parsed := new(response)
+	assert.NoError(t, json.Unmarshal(resp.Body.Bytes(), parsed))
+	assert.True(t, len(parsed.AccessToken) > 10)
+	assert.True(t, len(parsed.RefreshToken) > 10)
+
+	// use wrong client_secret
+	req = NewRequestWithValues(t, "POST", "/login/oauth/access_token", map[string]string{
+		"grant_type":    "authorization_code",
+		"redirect_uri":  "a",
+		"code":          "authcode",
+		"code_verifier": "N1Zo9-8Rfwhkt68r1r29ty8YwIraXR8eh_1Qwxg7yQXsonBt", // test PKCE additionally
+	})
+	req.Header.Add("Authorization", "Basic ZGE3ZGEzYmEtOWExMy00MTY3LTg1NmYtMzg5OWRlMGIwMTM4OmJsYWJsYQ==")
+	resp = MakeRequest(t, req, 400)
+
+	// missing header
+	req = NewRequestWithValues(t, "POST", "/login/oauth/access_token", map[string]string{
+		"grant_type":    "authorization_code",
+		"redirect_uri":  "a",
+		"code":          "authcode",
+		"code_verifier": "N1Zo9-8Rfwhkt68r1r29ty8YwIraXR8eh_1Qwxg7yQXsonBt", // test PKCE additionally
+	})
+	resp = MakeRequest(t, req, 400)
+}
diff --git a/routers/user/oauth.go b/routers/user/oauth.go
index dbb3c4a391..110fa93b3d 100644
--- a/routers/user/oauth.go
+++ b/routers/user/oauth.go
@@ -5,8 +5,10 @@
 package user
 
 import (
+	"encoding/base64"
 	"fmt"
 	"net/url"
+	"strings"
 
 	"github.com/dgrijalva/jwt-go"
 	"github.com/go-macaron/binding"
@@ -305,6 +307,30 @@ func GrantApplicationOAuth(ctx *context.Context, form auth.GrantApplicationForm)
 
 // AccessTokenOAuth manages all access token requests by the client
 func AccessTokenOAuth(ctx *context.Context, form auth.AccessTokenForm) {
+	if form.ClientID == "" {
+		authHeader := ctx.Req.Header.Get("Authorization")
+		authContent := strings.SplitN(authHeader, " ", 2)
+		if len(authContent) == 2 && authContent[0] == "Basic" {
+			payload, err := base64.StdEncoding.DecodeString(authContent[1])
+			if err != nil {
+				handleAccessTokenError(ctx, AccessTokenError{
+					ErrorCode:        AccessTokenErrorCodeInvalidRequest,
+					ErrorDescription: "cannot parse basic auth header",
+				})
+				return
+			}
+			pair := strings.SplitN(string(payload), ":", 2)
+			if len(pair) != 2 {
+				handleAccessTokenError(ctx, AccessTokenError{
+					ErrorCode:        AccessTokenErrorCodeInvalidRequest,
+					ErrorDescription: "cannot parse basic auth header",
+				})
+				return
+			}
+			form.ClientID = pair[0]
+			form.ClientSecret = pair[1]
+		}
+	}
 	switch form.GrantType {
 	case "refresh_token":
 		handleRefreshToken(ctx, form)
@@ -361,7 +387,7 @@ func handleAuthorizationCode(ctx *context.Context, form auth.AccessTokenForm) {
 	if err != nil {
 		handleAccessTokenError(ctx, AccessTokenError{
 			ErrorCode:        AccessTokenErrorCodeInvalidClient,
-			ErrorDescription: "cannot load client",
+			ErrorDescription: fmt.Sprintf("cannot load client with client id: '%s'", form.ClientID),
 		})
 		return
 	}