feat: get access token automatically (#261)

Author: spyth

README.md

@@ -119,8 +119,6 @@ import "github.com/plutov/paypal/v4"
 // Create a client instance
 c, err := paypal.NewClient("clientID", "secretID", paypal.APIBaseSandBox)
 c.SetLog(os.Stdout) // Set log to terminal stdout
-
-accessToken, err := c.GetAccessToken(context.Background())
 ```
 
 ## Get authorization by ID

client.go

@@ -143,18 +143,16 @@ func (c *Client) SendWithAuth(req *http.Request, v interface{}) error {
 	// Note: Here we do not want to `defer c.Unlock()` because we need `c.Send(...)`
 	// to happen outside of the locked section.
 
-	if c.Token != nil {
-		if !c.tokenExpiresAt.IsZero() && c.tokenExpiresAt.Sub(time.Now()) < RequestNewTokenBeforeExpiresIn {
-			// c.Token will be updated in GetAccessToken call
-			if _, err := c.GetAccessToken(req.Context()); err != nil {
-				// c.Unlock()
-				c.mu.Unlock()
-				return err
-			}
+	if c.Token == nil || (!c.tokenExpiresAt.IsZero() && time.Until(c.tokenExpiresAt) < RequestNewTokenBeforeExpiresIn) {
+		// c.Token will be updated in GetAccessToken call
+		if _, err := c.GetAccessToken(req.Context()); err != nil {
+			// c.Unlock()
+			c.mu.Unlock()
+			return err
 		}
-
-		req.Header.Set("Authorization", "Bearer "+c.Token.Token)
 	}
+
+	req.Header.Set("Authorization", "Bearer "+c.Token.Token)
 	// Unlock the client mutex before sending the request, this allows multiple requests
 	// to be in progress at the same time.
 	// c.Unlock()

client_test.go

@@ -65,19 +65,15 @@ func (c *Client) sendWithAuth(req *http.Request, v interface{}) error {
 		err := errors.New("TryLock succeeded inside sendWithAuth with mutex locked")
 		return err
 	}
-
-	if c.Token != nil {
-		if !c.tokenExpiresAt.IsZero() && c.tokenExpiresAt.Sub(time.Now()) < RequestNewTokenBeforeExpiresIn {
-			// c.Token will be updated in GetAccessToken call
-			if _, err := c.GetAccessToken(req.Context()); err != nil {
-				// c.Unlock()
-				c.mu.Unlock()
-				return err
-			}
+	if c.Token == nil || (!c.tokenExpiresAt.IsZero() && time.Until(c.tokenExpiresAt) < RequestNewTokenBeforeExpiresIn) {
+		// c.Token will be updated in GetAccessToken call
+		if _, err := c.GetAccessToken(req.Context()); err != nil {
+			// c.Unlock()
+			c.mu.Unlock()
+			return err
 		}
-
-		req.Header.Set("Authorization", "Bearer "+c.Token.Token)
 	}
+	req.Header.Set("Authorization", "Bearer "+c.Token.Token)
 	// Unlock the client mutex before sending the request, this allows multiple requests
 	// to be in progress at the same time.
 	// c.Unlock()