Add CustomTokenSource for custom token validation

This commit adds CustomTokenSource which allows the user to specify a
function which accepts a token validation function. This also changes
the internal implementation of ReuseTokenSource to use CustomTokenSource
under the hood while keeping the same external API.

Author: fharding1

oauth2.go

@@ -244,10 +244,7 @@ func (c *Config) TokenSource(ctx context.Context, t *Token) TokenSource {
 	if t != nil {
 		tkr.refreshToken = t.RefreshToken
 	}
-	return &reuseTokenSource{
-		t:   t,
-		new: tkr,
-	}
+	return ReuseTokenSource(t, tkr)
 }
 
 // tokenRefresher is a TokenSource that makes "grant_type"=="refresh_token"
@@ -281,24 +278,64 @@ func (tf *tokenRefresher) Token() (*Token, error) {
 	return tk, err
 }
 
-// reuseTokenSource is a TokenSource that holds a single token in memory
-// and validates its expiry before each call to retrieve it with
-// Token. If it's expired, it will be auto-refreshed using the
-// new TokenSource.
-type reuseTokenSource struct {
-	new TokenSource // called when t is expired.
+// StaticTokenSource returns a TokenSource that always returns the same token.
+// Because the provided token t is never refreshed, StaticTokenSource is only
+// useful for tokens that never expire.
+func StaticTokenSource(t *Token) TokenSource {
+	return staticTokenSource{t}
+}
+
+// staticTokenSource is a TokenSource that always returns the same Token.
+type staticTokenSource struct {
+	t *Token
+}
+
+func (s staticTokenSource) Token() (*Token, error) {
+	return s.t, nil
+}
+
+// ValidFunc should return false when the passed token is invalid and true when
+// the token is valid. ValidFunc should NOT modify the token passed to it.
+type ValidFunc func(t *Token) bool
+
+// CustomTokenSource returns a TokenSource which repeatedly returns the
+// same token as long as ValidFunc returns true, starting with t.
+// When ValidFunc returns false (the cached token is invalid), a new token
+// is obtained from src.
+func CustomTokenSource(t *Token, src TokenSource, validFunc ValidFunc) TokenSource {
+	// Don't wrap a customTokenSource in itself. That would work,
+	// but cause an unnecessary number of mutex operations.
+	// Just build the equivalent one.
+	if rt, ok := src.(*customTokenSource); ok {
+		if t == nil {
+			// Just use it directly.
+			return rt
+		}
+		src = rt.new
+	}
+	return &customTokenSource{
+		t:         t,
+		new:       src,
+		validFunc: validFunc,
+	}
+}
+
+type customTokenSource struct {
+	validFunc ValidFunc   // used for determining whether the token should be refreshed
+	new       TokenSource // called when validFunc returns invalid
 
 	mu sync.Mutex // guards t
 	t  *Token
 }
 
-// Token returns the current token if it's still valid, else will
-// refresh the current token (using r.Context for HTTP client
-// information) and return the new one.
-func (s *reuseTokenSource) Token() (*Token, error) {
+// Token returns a TokenSource that will return the current token so long as
+// ValidFunc returns that the token is valid, otherwise it will refresh the
+// current token (using r.Context for HTTP client information) and return the
+// new one.
+func (s *customTokenSource) Token() (*Token, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	if s.t.Valid() {
+	if s.validFunc(s.t) {
 		return s.t, nil
 	}
 	t, err := s.new.Token()
@@ -309,22 +346,6 @@ func (s *reuseTokenSource) Token() (*Token, error) {
 	return t, nil
 }
 
-// StaticTokenSource returns a TokenSource that always returns the same token.
-// Because the provided token t is never refreshed, StaticTokenSource is only
-// useful for tokens that never expire.
-func StaticTokenSource(t *Token) TokenSource {
-	return staticTokenSource{t}
-}
-
-// staticTokenSource is a TokenSource that always returns the same Token.
-type staticTokenSource struct {
-	t *Token
-}
-
-func (s staticTokenSource) Token() (*Token, error) {
-	return s.t, nil
-}
-
 // HTTPClient is the context key to use with golang.org/x/net/context's
 // WithValue function to associate an *http.Client value with a context.
 var HTTPClient internal.ContextKey
@@ -364,18 +385,7 @@ func NewClient(ctx context.Context, src TokenSource) *http.Client {
 // means it's always safe to wrap ReuseTokenSource around any other
 // TokenSource without adverse effects.
 func ReuseTokenSource(t *Token, src TokenSource) TokenSource {
-	// Don't wrap a reuseTokenSource in itself. That would work,
-	// but cause an unnecessary number of mutex operations.
-	// Just build the equivalent one.
-	if rt, ok := src.(*reuseTokenSource); ok {
-		if t == nil {
-			// Just use it directly.
-			return rt
-		}
-		src = rt.new
-	}
-	return &reuseTokenSource{
-		t:   t,
-		new: src,
-	}
+	return CustomTokenSource(t, src, func(t *Token) bool {
+		return t.Valid()
+	})
 }

oauth2_test.go

@@ -565,3 +565,59 @@ func TestConfigClientWithToken(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+type mockTokenSource struct {
+	nextToken *Token
+}
+
+func (s mockTokenSource) Token() (*Token, error) {
+	return s.nextToken, nil
+}
+
+func TestCustomTokenSource(t *testing.T) {
+	foobarToken := &Token{AccessToken: "foobar"}
+	barbazToken := &Token{AccessToken: "barbaz"}
+
+	testCases := []struct {
+		name          string
+		t             *Token
+		src           TokenSource
+		validToken    bool
+		expectedToken *Token
+	}{
+		{
+			name:          "invalid token",
+			t:             foobarToken,
+			src:           mockTokenSource{nextToken: barbazToken},
+			validToken:    false,
+			expectedToken: barbazToken,
+		},
+		{
+			name:          "valid token",
+			t:             foobarToken,
+			src:           mockTokenSource{nextToken: barbazToken},
+			validToken:    true,
+			expectedToken: foobarToken,
+		},
+	}
+
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			validFunc := func(t *Token) bool { return tt.validToken }
+			ts := CustomTokenSource(tt.t, tt.src, validFunc)
+
+			// the same expected token should always be returned no matter how many iterations
+			// we go through since the validfunc returns a constant value
+			for i := 0; i < 3; i++ {
+				newToken, err := ts.Token()
+				if err != nil {
+					t.Errorf("did not expect an error but got: %v", err)
+				}
+
+				if tt.expectedToken != newToken {
+					t.Errorf("expected token %v, but got %v", tt.expectedToken, newToken)
+				}
+			}
+		})
+	}
+}