oauth2: perform caching ops at the transport level

google/google.go

@@ -146,10 +146,3 @@ func (c *ComputeEngineConfig) FetchToken(existing *oauth2.Token) (token *oauth2.
 	}
 	return
 }
-
-// Cache returns nil. On Google Compute Engine, access tokens are
-// retrieved from the metaserver, no other persistence layer is
-// required.
-func (c *ComputeEngineConfig) Cache() oauth2.Cache {
-	return nil
-}

jwt.go

@@ -56,7 +56,6 @@ type JWTConfig struct {
 	opts      *JWTOptions
 	aud       string
 	signature []byte
-	cache     Cache
 }
 
 // NewTransport creates a transport that is authorize with the
@@ -75,12 +74,7 @@ func (c *JWTConfig) NewTransportWithUser(user string) Transport {
 // token from the provided cache. If a token refreshing occurs, it
 // writes the newly fetched token back to the cache.
 func (c *JWTConfig) NewTransportWithCache(cache Cache) (Transport, error) {
-	token, err := cache.Read()
+	return NewAuthorizedTransportWithCache(c, cache)
-	if err != nil {
-		return nil, err
-	}
-	c.cache = cache
-	return NewAuthorizedTransport(c, token), nil
 }
 
 // fetchToken retrieves a new access token and updates the existing token
@@ -151,8 +145,3 @@ func (c *JWTConfig) FetchToken(existing *Token) (token *Token, err error) {
 	token.Expiry = time.Now().Add(time.Duration(b.ExpiresIn) * time.Second)
 	return
 }
-
-// Cache returns a cache if specified, otherwise nil.
-func (c *JWTConfig) Cache() Cache {
-	return c.cache
-}

oauth2.go

@@ -64,8 +64,6 @@ type TokenFetcher interface {
 	// If the implementation doesn't know how to retrieve a new token,
 	// it returns an error.
 	FetchToken(existing *Token) (*Token, error)
-	// Cache returns the Cache implementation to read/persist user tokens.
-	Cache() Cache
 }
 
 // Options represents options to provide OAuth 2.0 client credentials
@@ -130,8 +128,6 @@ type Config struct {
 	authURL string
 	// TokenURL is the URL used to retrieve OAuth tokens.
 	tokenURL string
-
-	cache Cache
 }
 
 // AuthCodeURL returns a URL to OAuth 2.0 provider's consent page
@@ -187,12 +183,7 @@ func (c *Config) NewTransportWithCode(exchangeCode string) (Transport, error) {
 // token from the provided cache. If a token refreshing occurs, it
 // writes the newly fetched token back to the cache.
 func (c *Config) NewTransportWithCache(cache Cache) (Transport, error) {
-	token, err := cache.Read()
+	return NewAuthorizedTransportWithCache(c, cache)
-	if err != nil {
-		return nil, err
-	}
-	c.cache = cache
-	return NewAuthorizedTransport(c, token), nil
 }
 
 // Exchange exchanges the exchange code with the OAuth 2.0 provider
@@ -225,11 +216,6 @@ func (c *Config) FetchToken(existing *Token) (*Token, error) {
 	return existing, err
 }
 
-// Cache returns a cache if specified, otherwise nil.
-func (c *Config) Cache() Cache {
-	return c.cache
-}
-
 // Checks if all required configuration fields have non-zero values.
 func (c *Config) validate() error {
 	if c.opts.ClientID == "" {

transport.go

@@ -76,6 +76,9 @@ type Transport interface {
 }
 
 type authorizedTransport struct {
+	// Cache to persist changes to the token that
+	// authorizes the current transport.
+	cache   Cache
 	fetcher TokenFetcher
 	token   *Token
 
@@ -90,6 +93,15 @@ func NewAuthorizedTransport(fetcher TokenFetcher, token *Token) Transport {
 	return &authorizedTransport{fetcher: fetcher, token: token}
 }
 
+func NewAuthorizedTransportWithCache(fetcher TokenFetcher, cache Cache) (transport Transport, err error) {
+	var token *Token
+	if token, err = cache.Read(); err != nil {
+		return
+	}
+	transport = &authorizedTransport{fetcher: fetcher, cache: cache, token: token}
+	return
+}
+
 // RoundTrip authorizes the request with the existing token.
 // If token is expired, tries to refresh/fetch a new token.
 func (t *authorizedTransport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
@@ -160,8 +172,8 @@ func (t *authorizedTransport) RefreshToken() error {
 	}
 
 	t.token = token
-	if c := t.fetcher.Cache(); c != nil {
+	if t.cache != nil {
-		c.Write(token)
+		t.cache.Write(token)
 	}
 
 	return nil