internal: optionally skip urlencoding client id and secret in header

clientcredentials/clientcredentials_test.go

@@ -136,3 +136,56 @@ func TestTokenRefreshRequest(t *testing.T) {
 	c := conf.Client(context.Background())
 	c.Get(ts.URL + "/somethingelse")
 }
+
+func TestTokenRequestWithoutCredentialsEncoding(t *testing.T) {
+	attempt := 1
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if attempt != 3 {
+			w.WriteHeader(401)
+			attempt++
+			return
+		}
+		if r.URL.String() != "/token" {
+			t.Errorf("authenticate client request URL = %q; want %q", r.URL, "/token")
+		}
+		headerAuth := r.Header.Get("Authorization")
+		if headerAuth != "Basic Q0xJRU5UX0lEISs6Q0xJRU5UX1NFQ1JFVCYrQA==" {
+			t.Errorf("Unexpected authorization header, %v is found.", headerAuth)
+		}
+		if got, want := r.Header.Get("Content-Type"), "application/x-www-form-urlencoded"; got != want {
+			t.Errorf("Content-Type header = %q; want %q", got, want)
+		}
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			r.Body.Close()
+		}
+		if err != nil {
+			t.Errorf("failed reading request body: %s.", err)
+		}
+		if string(body) != "grant_type=client_credentials&scope=scope" {
+			t.Errorf("payload = %q; want %q", string(body), "grant_type=client_credentials&scope=scope")
+		}
+		w.Header().Set("Content-Type", "application/x-www-form-urlencoded")
+		w.Write([]byte("access_token=90d64460d14870c08c81352a05dedd3465940a7c&token_type=bearer"))
+	}))
+	defer ts.Close()
+	conf := &Config{
+		ClientID:     "CLIENT_ID!+",
+		ClientSecret: "CLIENT_SECRET&+@",
+		Scopes:       []string{"scope"},
+		TokenURL:     ts.URL + "/token",
+	}
+	tok, err := conf.Token(context.Background())
+	if err != nil {
+		t.Error(err)
+	}
+	if !tok.Valid() {
+		t.Fatalf("token invalid. got: %#v", tok)
+	}
+	if tok.AccessToken != "90d64460d14870c08c81352a05dedd3465940a7c" {
+		t.Errorf("Access token = %q; want %q", tok.AccessToken, "90d64460d14870c08c81352a05dedd3465940a7c")
+	}
+	if tok.TokenType != "bearer" {
+		t.Errorf("token type = %q; want %q", tok.TokenType, "bearer")
+	}
+}

internal/token.go

@@ -10,7 +10,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
 	"mime"
 	"net/http"
@@ -111,9 +110,10 @@ func RegisterBrokenAuthHeaderProvider(tokenURL string) {}
 type AuthStyle int
 
 const (
-	AuthStyleUnknown  AuthStyle = 0
-	AuthStyleInParams AuthStyle = 1
-	AuthStyleInHeader AuthStyle = 2
+	AuthStyleUnknown                 AuthStyle = 0
+	AuthStyleInParams                AuthStyle = 1
+	AuthStyleInHeader                AuthStyle = 2
+	AuthStyleInHeaderWithoutEncoding AuthStyle = 3
 )
 
 // LazyAuthStyleCache is a backwards compatibility compromise to let Configs
@@ -197,6 +197,8 @@ func newTokenRequest(tokenURL, clientID, clientSecret string, v url.Values, auth
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 	if authStyle == AuthStyleInHeader {
 		req.SetBasicAuth(url.QueryEscape(clientID), url.QueryEscape(clientSecret))
+	} else if authStyle == AuthStyleInHeaderWithoutEncoding {
+		req.SetBasicAuth(clientID, clientSecret)
 	}
 	return req, nil
 }
@@ -240,6 +242,15 @@ func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string,
 		authStyle = AuthStyleInParams // the second way we'll try
 		req, _ = newTokenRequest(tokenURL, clientID, clientSecret, v, authStyle)
 		token, err = doTokenRoundTrip(ctx, req)
+
+		// although https://tools.ietf.org/html/rfc6749#section-2.3.1 states that
+		// clientID & clientSecret must be urlencoded in the authorization header
+		// there are some sites that don't do this thus resulting in authentication failure
+		if err != nil {
+			authStyle = AuthStyleInHeaderWithoutEncoding
+			req, _ = newTokenRequest(tokenURL, clientID, clientSecret, v, authStyle)
+			token, err = doTokenRoundTrip(ctx, req)
+		}
 	}
 	if needsAuthStyleProbe && err == nil {
 		styleCache.setAuthStyle(tokenURL, authStyle)
@@ -257,7 +268,7 @@ func doTokenRoundTrip(ctx context.Context, req *http.Request) (*Token, error) {
 	if err != nil {
 		return nil, err
 	}
-	body, err := ioutil.ReadAll(io.LimitReader(r.Body, 1<<20))
+	body, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
 	r.Body.Close()
 	if err != nil {
 		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)

oauth2.go

@@ -103,6 +103,10 @@ const (
 	// using HTTP Basic Authorization. This is an optional style
 	// described in the OAuth2 RFC 6749 section 2.3.1.
 	AuthStyleInHeader AuthStyle = 2
+
+	// AuthStyleInHeaderWithoutEncoding is similar to the AuthStyleInHeader,
+	// but it doesn't url encode client_id and client_password
+	AuthStyleInHeaderWithoutEncoding AuthStyle = 3
 )
 
 var (