go.mod: update golang.org/x dependencies

Update golang.org/x dependencies to their latest tagged versions.

Change-Id: I2fb95ca59417e20377bc315094221fa7165128c8
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/525675
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Gopher Robot <gobot@golang.org>

clientcredentials/clientcredentials.go

@@ -47,6 +47,10 @@ type Config struct {
 	// client ID & client secret sent. The zero value means to
 	// auto-detect.
 	AuthStyle oauth2.AuthStyle
+
+	// authStyleCache caches which auth style to use when Endpoint.AuthStyle is
+	// the zero value (AuthStyleAutoDetect).
+	authStyleCache internal.LazyAuthStyleCache
 }
 
 // Token uses client credentials to retrieve a token.
@@ -103,7 +107,7 @@ func (c *tokenSource) Token() (*oauth2.Token, error) {
 		v[k] = p
 	}
 
-	tk, err := internal.RetrieveToken(c.ctx, c.conf.ClientID, c.conf.ClientSecret, c.conf.TokenURL, v, internal.AuthStyle(c.conf.AuthStyle))
+	tk, err := internal.RetrieveToken(c.ctx, c.conf.ClientID, c.conf.ClientSecret, c.conf.TokenURL, v, internal.AuthStyle(c.conf.AuthStyle), c.conf.authStyleCache.Get())
 	if err != nil {
 		if rErr, ok := err.(*internal.RetrieveError); ok {
 			return nil, (*oauth2.RetrieveError)(rErr)

clientcredentials/clientcredentials_test.go

@@ -12,8 +12,6 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"testing"
-
-	"golang.org/x/oauth2/internal"
 )
 
 func newConf(serverURL string) *Config {
@@ -114,7 +112,6 @@ func TestTokenRequest(t *testing.T) {
 }
 
 func TestTokenRefreshRequest(t *testing.T) {
-	internal.ResetAuthCache()
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.String() == "/somethingelse" {
 			return

go.mod

@@ -1,15 +1,16 @@
 module golang.org/x/oauth2
 
-go 1.17
+go 1.18
 
 require (
-	cloud.google.com/go/compute/metadata v0.2.0
+	cloud.google.com/go/compute/metadata v0.2.3
-	github.com/google/go-cmp v0.5.8
+	github.com/google/go-cmp v0.5.9
 	google.golang.org/appengine v1.6.7
 )
 
 require (
-	github.com/golang/protobuf v1.5.2 // indirect
+	cloud.google.com/go/compute v1.20.1 // indirect
-	golang.org/x/net v0.9.0 // indirect
+	github.com/golang/protobuf v1.5.3 // indirect
-	google.golang.org/protobuf v1.28.0 // indirect
+	golang.org/x/net v0.15.0 // indirect
+	google.golang.org/protobuf v1.31.0 // indirect
 )

go.sum

@@ -1,53 +1,26 @@
-cloud.google.com/go/compute/metadata v0.2.0 h1:nBbNSZyDpkNlo3DepaaLKVuO7ClyifSAmNloSCZrHnQ=
+cloud.google.com/go/compute v1.20.1 h1:6aKEtlUiwEpJzM001l0yFkpXmUVXaN8W+fbkb2AZNbg=
-cloud.google.com/go/compute/metadata v0.2.0/go.mod h1:zFmK7XCadkQkj6TtorcaGlCW1hT1fIilQDwofLpJ20k=
+cloud.google.com/go/compute v1.20.1/go.mod h1:4tCnrn48xsqlwSAiLf1HXMQk8CONslYbdiEZc9FEIbM=
+cloud.google.com/go/compute/metadata v0.2.3 h1:mg4jlk7mCAj6xXp9UJ4fjI9VUI5rubuGBW5aJ7UnBMY=
+cloud.google.com/go/compute/metadata v0.2.3/go.mod h1:VAV5nSsACxMJvgaAuX6Pk2AawlZn8kiOGuCv6gTkwuA=
 github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
-github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw=
+github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
-github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/golang/protobuf v1.5.3/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
-github.com/google/go-cmp v0.5.8 h1:e6P7q2lk1O+qJJb4BtCQXlK8vWEO8V1ZeuEdJNOqZyg=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
-github.com/google/go-cmp v0.5.8/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
-github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
-golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
-golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.0.0-20190603091049-60506f45cf65/go.mod h1:HSz+uSET+XFnRR8LxR5pz3Of3rY3CfYBVs4xY44aLks=
-golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
-golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
+golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
-golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
-golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
-golang.org/x/net v0.9.0 h1:aWJ/m6xSmxWBx+V0XRHTlrYrPG56jKsLdTFmsSsCzOM=
-golang.org/x/net v0.9.0/go.mod h1:d48xBJpPfHeWQsugry2m+kC02ZBRGRgulfHnEXEuWns=
-golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
-golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
-golang.org/x/term v0.7.0/go.mod h1:P32HKFT3hSsZrRxla30E9HqToFYAQPCMs/zFMBUFqPY=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
-golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
-golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
-golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
-golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
-golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
-golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/appengine v1.6.7 h1:FZR1q0exgwxzPzp/aF+VccGrSfxfPpkBqjIIEq3ru6c=
 google.golang.org/appengine v1.6.7/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
 google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
-google.golang.org/protobuf v1.28.0 h1:w43yiav+6bVFTBQFZX0r7ipe9JQ1QsbMgHwbBziscLw=
+google.golang.org/protobuf v1.31.0 h1:g0LDEJHgrBl9N9r17Ru3sqWhkIx2NB67okBHPwC7hs8=
-google.golang.org/protobuf v1.28.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
+google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=

google/appengine_gen1.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build appengine
-// +build appengine
 
 // This file applies to App Engine first generation runtimes (<= Go 1.9).
 

google/appengine_gen2_flex.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !appengine
-// +build !appengine
 
 // This file applies to App Engine second generation runtimes (>= Go 1.11) and App Engine flexible.
 

google/default.go

@@ -8,7 +8,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -142,10 +141,8 @@ func FindDefaultCredentialsWithParams(ctx context.Context, params CredentialsPar
 
 	// Second, try a well-known file.
 	filename := wellKnownFile()
-	if creds, err := readCredentialsFile(ctx, filename, params); err == nil {
+	if b, err := os.ReadFile(filename); err == nil {
-		return creds, nil
+		return CredentialsFromJSONWithParams(ctx, b, params)
-	} else if !os.IsNotExist(err) {
-		return nil, fmt.Errorf("google: error getting credentials using well-known file (%v): %v", filename, err)
 	}
 
 	// Third, if we're on a Google App Engine standard first generation runtime (<= Go 1.9)
@@ -231,7 +228,7 @@ func wellKnownFile() string {
 }
 
 func readCredentialsFile(ctx context.Context, filename string, params CredentialsParams) (*Credentials, error) {
-	b, err := ioutil.ReadFile(filename)
+	b, err := os.ReadFile(filename)
 	if err != nil {
 		return nil, err
 	}

internal/client_appengine.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build appengine
-// +build appengine
 
 package internal
 

internal/oauth2.go

@@ -14,7 +14,7 @@ import (
 
 // ParseKey converts the binary contents of a private key file
 // to an *rsa.PrivateKey. It detects whether the private key is in a
-// PEM container or not. If so, it extracts the the private key
+// PEM container or not. If so, it extracts the private key
 // from PEM container before conversion. It only supports PEM
 // containers with no passphrase.
 func ParseKey(key []byte) (*rsa.PrivateKey, error) {

internal/token.go

@@ -18,6 +18,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 )
 
@@ -55,12 +56,18 @@ type Token struct {
 }
 
 // tokenJSON is the struct representing the HTTP response from OAuth2
-// providers returning a token in JSON form.
+// providers returning a token or error in JSON form.
+// https://datatracker.ietf.org/doc/html/rfc6749#section-5.1
 type tokenJSON struct {
 	AccessToken  string         `json:"access_token"`
 	TokenType    string         `json:"token_type"`
 	RefreshToken string         `json:"refresh_token"`
 	ExpiresIn    expirationTime `json:"expires_in"` // at least PayPal returns string, while most return number
+	// error fields
+	// https://datatracker.ietf.org/doc/html/rfc6749#section-5.2
+	ErrorCode        string `json:"error"`
+	ErrorDescription string `json:"error_description"`
+	ErrorURI         string `json:"error_uri"`
 }
 
 func (e *tokenJSON) expiry() (t time.Time) {
@@ -109,41 +116,60 @@ const (
 	AuthStyleInHeader AuthStyle = 2
 )
 
-// authStyleCache is the set of tokenURLs we've successfully used via
+// LazyAuthStyleCache is a backwards compatibility compromise to let Configs
+// have a lazily-initialized AuthStyleCache.
+//
+// The two users of this, oauth2.Config and oauth2/clientcredentials.Config,
+// both would ideally just embed an unexported AuthStyleCache but because both
+// were historically allowed to be copied by value we can't retroactively add an
+// uncopyable Mutex to them.
+//
+// We could use an atomic.Pointer, but that was added recently enough (in Go
+// 1.18) that we'd break Go 1.17 users where the tests as of 2023-08-03
+// still pass. By using an atomic.Value, it supports both Go 1.17 and
+// copying by value, even if that's not ideal.
+type LazyAuthStyleCache struct {
+	v atomic.Value // of *AuthStyleCache
+}
+
+func (lc *LazyAuthStyleCache) Get() *AuthStyleCache {
+	if c, ok := lc.v.Load().(*AuthStyleCache); ok {
+		return c
+	}
+	c := new(AuthStyleCache)
+	if !lc.v.CompareAndSwap(nil, c) {
+		c = lc.v.Load().(*AuthStyleCache)
+	}
+	return c
+}
+
+// AuthStyleCache is the set of tokenURLs we've successfully used via
 // RetrieveToken and which style auth we ended up using.
 // It's called a cache, but it doesn't (yet?) shrink. It's expected that
 // the set of OAuth2 servers a program contacts over time is fixed and
 // small.
-var authStyleCache struct {
+type AuthStyleCache struct {
-	sync.Mutex
+	mu sync.Mutex
-	m map[string]AuthStyle // keyed by tokenURL
+	m  map[string]AuthStyle // keyed by tokenURL
-}
-
-// ResetAuthCache resets the global authentication style cache used
-// for AuthStyleUnknown token requests.
-func ResetAuthCache() {
-	authStyleCache.Lock()
-	defer authStyleCache.Unlock()
-	authStyleCache.m = nil
 }
 
 // lookupAuthStyle reports which auth style we last used with tokenURL
 // when calling RetrieveToken and whether we have ever done so.
-func lookupAuthStyle(tokenURL string) (style AuthStyle, ok bool) {
+func (c *AuthStyleCache) lookupAuthStyle(tokenURL string) (style AuthStyle, ok bool) {
-	authStyleCache.Lock()
+	c.mu.Lock()
-	defer authStyleCache.Unlock()
+	defer c.mu.Unlock()
-	style, ok = authStyleCache.m[tokenURL]
+	style, ok = c.m[tokenURL]
 	return
 }
 
 // setAuthStyle adds an entry to authStyleCache, documented above.
-func setAuthStyle(tokenURL string, v AuthStyle) {
+func (c *AuthStyleCache) setAuthStyle(tokenURL string, v AuthStyle) {
-	authStyleCache.Lock()
+	c.mu.Lock()
-	defer authStyleCache.Unlock()
+	defer c.mu.Unlock()
-	if authStyleCache.m == nil {
+	if c.m == nil {
-		authStyleCache.m = make(map[string]AuthStyle)
+		c.m = make(map[string]AuthStyle)
 	}
-	authStyleCache.m[tokenURL] = v
+	c.m[tokenURL] = v
 }
 
 // newTokenRequest returns a new *http.Request to retrieve a new token
@@ -183,10 +209,10 @@ func cloneURLValues(v url.Values) url.Values {
 	return v2
 }
 
-func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string, v url.Values, authStyle AuthStyle) (*Token, error) {
+func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string, v url.Values, authStyle AuthStyle, styleCache *AuthStyleCache) (*Token, error) {
 	needsAuthStyleProbe := authStyle == 0
 	if needsAuthStyleProbe {
-		if style, ok := lookupAuthStyle(tokenURL); ok {
+		if style, ok := styleCache.lookupAuthStyle(tokenURL); ok {
 			authStyle = style
 			needsAuthStyleProbe = false
 		} else {
@@ -216,7 +242,7 @@ func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string,
 		token, err = doTokenRoundTrip(ctx, req)
 	}
 	if needsAuthStyleProbe && err == nil {
-		setAuthStyle(tokenURL, authStyle)
+		styleCache.setAuthStyle(tokenURL, authStyle)
 	}
 	// Don't overwrite `RefreshToken` with an empty value
 	// if this was a token refreshing request.
@@ -236,21 +262,29 @@ func doTokenRoundTrip(ctx context.Context, req *http.Request) (*Token, error) {
 	if err != nil {
 		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
 	}
-	if code := r.StatusCode; code < 200 || code > 299 {
+
-		return nil, &RetrieveError{
+	failureStatus := r.StatusCode < 200 || r.StatusCode > 299
-			Response: r,
+	retrieveError := &RetrieveError{
-			Body:     body,
+		Response: r,
-		}
+		Body:     body,
+		// attempt to populate error detail below
 	}
 
 	var token *Token
 	content, _, _ := mime.ParseMediaType(r.Header.Get("Content-Type"))
 	switch content {
 	case "application/x-www-form-urlencoded", "text/plain":
+		// some endpoints return a query string
 		vals, err := url.ParseQuery(string(body))
 		if err != nil {
-			return nil, err
+			if failureStatus {
+				return nil, retrieveError
+			}
+			return nil, fmt.Errorf("oauth2: cannot parse response: %v", err)
 		}
+		retrieveError.ErrorCode = vals.Get("error")
+		retrieveError.ErrorDescription = vals.Get("error_description")
+		retrieveError.ErrorURI = vals.Get("error_uri")
 		token = &Token{
 			AccessToken:  vals.Get("access_token"),
 			TokenType:    vals.Get("token_type"),
@@ -265,8 +299,14 @@ func doTokenRoundTrip(ctx context.Context, req *http.Request) (*Token, error) {
 	default:
 		var tj tokenJSON
 		if err = json.Unmarshal(body, &tj); err != nil {
-			return nil, err
+			if failureStatus {
+				return nil, retrieveError
+			}
+			return nil, fmt.Errorf("oauth2: cannot parse json: %v", err)
 		}
+		retrieveError.ErrorCode = tj.ErrorCode
+		retrieveError.ErrorDescription = tj.ErrorDescription
+		retrieveError.ErrorURI = tj.ErrorURI
 		token = &Token{
 			AccessToken:  tj.AccessToken,
 			TokenType:    tj.TokenType,
@@ -276,17 +316,37 @@ func doTokenRoundTrip(ctx context.Context, req *http.Request) (*Token, error) {
 		}
 		json.Unmarshal(body, &token.Raw) // no error checks for optional fields
 	}
+	// according to spec, servers should respond status 400 in error case
+	// https://www.rfc-editor.org/rfc/rfc6749#section-5.2
+	// but some unorthodox servers respond 200 in error case
+	if failureStatus || retrieveError.ErrorCode != "" {
+		return nil, retrieveError
+	}
 	if token.AccessToken == "" {
 		return nil, errors.New("oauth2: server response missing access_token")
 	}
 	return token, nil
 }
 
+// mirrors oauth2.RetrieveError
 type RetrieveError struct {
-	Response *http.Response
+	Response         *http.Response
-	Body     []byte
+	Body             []byte
+	ErrorCode        string
+	ErrorDescription string
+	ErrorURI         string
 }
 
 func (r *RetrieveError) Error() string {
+	if r.ErrorCode != "" {
+		s := fmt.Sprintf("oauth2: %q", r.ErrorCode)
+		if r.ErrorDescription != "" {
+			s += fmt.Sprintf(" %q", r.ErrorDescription)
+		}
+		if r.ErrorURI != "" {
+			s += fmt.Sprintf(" %q", r.ErrorURI)
+		}
+		return s
+	}
 	return fmt.Sprintf("oauth2: cannot fetch token: %v\nResponse: %s", r.Response.Status, r.Body)
 }

internal/token_test.go

@@ -16,7 +16,7 @@ import (
 )
 
 func TestRetrieveToken_InParams(t *testing.T) {
-	ResetAuthCache()
+	styleCache := new(AuthStyleCache)
 	const clientID = "client-id"
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if got, want := r.FormValue("client_id"), clientID; got != want {
@@ -29,14 +29,14 @@ func TestRetrieveToken_InParams(t *testing.T) {
 		io.WriteString(w, `{"access_token": "ACCESS_TOKEN", "token_type": "bearer"}`)
 	}))
 	defer ts.Close()
-	_, err := RetrieveToken(context.Background(), clientID, "", ts.URL, url.Values{}, AuthStyleInParams)
+	_, err := RetrieveToken(context.Background(), clientID, "", ts.URL, url.Values{}, AuthStyleInParams, styleCache)
 	if err != nil {
 		t.Errorf("RetrieveToken = %v; want no error", err)
 	}
 }
 
 func TestRetrieveTokenWithContexts(t *testing.T) {
-	ResetAuthCache()
+	styleCache := new(AuthStyleCache)
 	const clientID = "client-id"
 
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -45,7 +45,7 @@ func TestRetrieveTokenWithContexts(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	_, err := RetrieveToken(context.Background(), clientID, "", ts.URL, url.Values{}, AuthStyleUnknown)
+	_, err := RetrieveToken(context.Background(), clientID, "", ts.URL, url.Values{}, AuthStyleUnknown, styleCache)
 	if err != nil {
 		t.Errorf("RetrieveToken (with background context) = %v; want no error", err)
 	}
@@ -58,7 +58,7 @@ func TestRetrieveTokenWithContexts(t *testing.T) {
 
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel()
-	_, err = RetrieveToken(ctx, clientID, "", cancellingts.URL, url.Values{}, AuthStyleUnknown)
+	_, err = RetrieveToken(ctx, clientID, "", cancellingts.URL, url.Values{}, AuthStyleUnknown, styleCache)
 	close(retrieved)
 	if err == nil {
 		t.Errorf("RetrieveToken (with cancelled context) = nil; want error")

oauth2.go

@@ -58,6 +58,10 @@ type Config struct {
 
 	// Scope specifies optional requested permissions.
 	Scopes []string
+
+	// authStyleCache caches which auth style to use when Endpoint.AuthStyle is
+	// the zero value (AuthStyleAutoDetect).
+	authStyleCache internal.LazyAuthStyleCache
 }
 
 // A TokenSource is anything that can return a token.

oauth2_test.go

@@ -15,8 +15,6 @@ import (
 	"net/url"
 	"testing"
 	"time"
-
-	"golang.org/x/oauth2/internal"
 )
 
 type mockTransport struct {
@@ -355,7 +353,6 @@ func TestExchangeRequest_BadResponseType(t *testing.T) {
 }
 
 func TestExchangeRequest_NonBasicAuth(t *testing.T) {
-	internal.ResetAuthCache()
 	tr := &mockTransport{
 		rt: func(r *http.Request) (w *http.Response, err error) {
 			headerAuth := r.Header.Get("Authorization")
@@ -427,7 +424,6 @@ func TestPasswordCredentialsTokenRequest(t *testing.T) {
 }
 
 func TestTokenRefreshRequest(t *testing.T) {
-	internal.ResetAuthCache()
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.String() == "/somethingelse" {
 			return
@@ -484,6 +480,7 @@ func TestTokenRetrieveError(t *testing.T) {
 			t.Errorf("Unexpected token refresh request URL, %v is found.", r.URL)
 		}
 		w.Header().Set("Content-type", "application/json")
+		// "The authorization server responds with an HTTP 400 (Bad Request)" https://www.rfc-editor.org/rfc/rfc6749#section-5.2
 		w.WriteHeader(http.StatusBadRequest)
 		w.Write([]byte(`{"error": "invalid_grant"}`))
 	}))
@@ -493,15 +490,47 @@ func TestTokenRetrieveError(t *testing.T) {
 	if err == nil {
 		t.Fatalf("got no error, expected one")
 	}
-	_, ok := err.(*RetrieveError)
+	re, ok := err.(*RetrieveError)
 	if !ok {
 		t.Fatalf("got %T error, expected *RetrieveError; error was: %v", err, err)
 	}
-	// Test error string for backwards compatibility
+	expected := `oauth2: "invalid_grant"`
-	expected := fmt.Sprintf("oauth2: cannot fetch token: %v\nResponse: %s", "400 Bad Request", `{"error": "invalid_grant"}`)
 	if errStr := err.Error(); errStr != expected {
 		t.Fatalf("got %#v, expected %#v", errStr, expected)
 	}
+	expected = "invalid_grant"
+	if re.ErrorCode != expected {
+		t.Fatalf("got %#v, expected %#v", re.ErrorCode, expected)
+	}
+}
+
+// TestTokenRetrieveError200 tests handling of unorthodox server that returns 200 in error case
+func TestTokenRetrieveError200(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.String() != "/token" {
+			t.Errorf("Unexpected token refresh request URL, %v is found.", r.URL)
+		}
+		w.Header().Set("Content-type", "application/json")
+		w.Write([]byte(`{"error": "invalid_grant"}`))
+	}))
+	defer ts.Close()
+	conf := newConf(ts.URL)
+	_, err := conf.Exchange(context.Background(), "exchange-code")
+	if err == nil {
+		t.Fatalf("got no error, expected one")
+	}
+	re, ok := err.(*RetrieveError)
+	if !ok {
+		t.Fatalf("got %T error, expected *RetrieveError; error was: %v", err, err)
+	}
+	expected := `oauth2: "invalid_grant"`
+	if errStr := err.Error(); errStr != expected {
+		t.Fatalf("got %#v, expected %#v", errStr, expected)
+	}
+	expected = "invalid_grant"
+	if re.ErrorCode != expected {
+		t.Fatalf("got %#v, expected %#v", re.ErrorCode, expected)
+	}
 }
 
 func TestRefreshToken_RefreshTokenReplacement(t *testing.T) {

token.go

@@ -164,7 +164,7 @@ func tokenFromInternal(t *internal.Token) *Token {
 // This token is then mapped from *internal.Token into an *oauth2.Token which is returned along
 // with an error..
 func retrieveToken(ctx context.Context, c *Config, v url.Values) (*Token, error) {
-	tk, err := internal.RetrieveToken(ctx, c.ClientID, c.ClientSecret, c.Endpoint.TokenURL, v, internal.AuthStyle(c.Endpoint.AuthStyle))
+	tk, err := internal.RetrieveToken(ctx, c.ClientID, c.ClientSecret, c.Endpoint.TokenURL, v, internal.AuthStyle(c.Endpoint.AuthStyle), c.authStyleCache.Get())
 	if err != nil {
 		if rErr, ok := err.(*internal.RetrieveError); ok {
 			return nil, (*RetrieveError)(rErr)
@@ -175,14 +175,31 @@ func retrieveToken(ctx context.Context, c *Config, v url.Values) (*Token, error)
 }
 
 // RetrieveError is the error returned when the token endpoint returns a
-// non-2XX HTTP status code.
+// non-2XX HTTP status code or populates RFC 6749's 'error' parameter.
+// https://datatracker.ietf.org/doc/html/rfc6749#section-5.2
 type RetrieveError struct {
 	Response *http.Response
 	// Body is the body that was consumed by reading Response.Body.
 	// It may be truncated.
 	Body []byte
+	// ErrorCode is RFC 6749's 'error' parameter.
+	ErrorCode string
+	// ErrorDescription is RFC 6749's 'error_description' parameter.
+	ErrorDescription string
+	// ErrorURI is RFC 6749's 'error_uri' parameter.
+	ErrorURI string
 }
 
 func (r *RetrieveError) Error() string {
+	if r.ErrorCode != "" {
+		s := fmt.Sprintf("oauth2: %q", r.ErrorCode)
+		if r.ErrorDescription != "" {
+			s += fmt.Sprintf(" %q", r.ErrorDescription)
+		}
+		if r.ErrorURI != "" {
+			s += fmt.Sprintf(" %q", r.ErrorURI)
+		}
+		return s
+	}
 	return fmt.Sprintf("oauth2: cannot fetch token: %v\nResponse: %s", r.Response.Status, r.Body)
 }