feat: support cache token

Author: SpectatorNan

cache.go

@@ -0,0 +1,16 @@
+package paypal
+
+import "context"
+
+type CacheToken struct {
+	RefreshToken string `json:"refresh_token"`
+	Token        string `json:"access_token"`
+	Type         string `json:"token_type"`
+	ExpiresIn    int64  `json:"expires_in"`
+	ExpiresAt    int64  `json:"expires_at"`
+}
+
+type Cache interface {
+	GetToken(ctx context.Context, clientId string) (*CacheToken, error)
+	SetToken(ctx context.Context, clientId string, token *CacheToken) error
+}

client.go

@@ -16,19 +16,48 @@ import (
 
 var ErrRateLimited = errors.New("rate limited")
 
+type Option func(o *Client) *Client
+
+func WithCache(cache Cache) Option {
+	return func(c *Client) *Client {
+		c.cache = cache
+		return c
+	}
+}
+
 // NewClient returns new Client struct
 // APIBase is a base API URL, for testing you can use paypal.APIBaseSandBox
-func NewClient(clientID string, secret string, APIBase string) (*Client, error) {
+func NewClient(ctx context.Context, clientID string, secret string, APIBase string, options ...Option) (*Client, error) {
 	if clientID == "" || secret == "" || APIBase == "" {
 		return nil, errors.New("ClientID, Secret and APIBase are required to create a Client")
 	}
 
-	return &Client{
+	cli := &Client{
 		Client:   &http.Client{},
 		ClientID: clientID,
 		Secret:   secret,
 		APIBase:  APIBase,
-	}, nil
+	}
+
+	for _, option := range options {
+		cli = option(cli)
+	}
+	cli.checkCacheToken(ctx)
+	return cli, nil
+}
+
+func (c *Client) checkCacheToken(ctx context.Context) {
+	if c.cache == nil {
+		return
+	}
+
+	token, err := c.cache.GetToken(ctx, c.ClientID)
+	if err != nil {
+		return
+	}
+	if token != nil && token.Token != "" {
+		c.SetAccessTokenWithExpiry(token.Token, token.ExpiresAt)
+	}
 }
 
 // GetAccessToken returns struct of TokenResponse
@@ -50,6 +79,20 @@ func (c *Client) GetAccessToken(ctx context.Context) (*TokenResponse, error) {
 	if response.Token != "" {
 		c.Token = response
 		c.tokenExpiresAt = time.Now().Add(time.Duration(response.ExpiresIn) * time.Second)
+
+		if c.cache != nil {
+			token := &CacheToken{
+				RefreshToken: response.RefreshToken,
+				Token:        response.Token,
+				Type:         response.Type,
+				ExpiresIn:    int64(response.ExpiresIn),
+				ExpiresAt:    c.tokenExpiresAt.Unix(),
+			}
+			err = c.cache.SetToken(ctx, c.ClientID, token)
+			if err != nil {
+				return response, err
+			}
+		}
 	}
 
 	return response, err
@@ -68,6 +111,16 @@ func (c *Client) SetAccessToken(token string) {
 	c.tokenExpiresAt = time.Time{}
 }
 
+// SetAccessTokenWithExpiry sets saved token to current client with expiry time
+func (c *Client) SetAccessTokenWithExpiry(token string, expiresAt int64) {
+	c.Token = &TokenResponse{
+		Token: token,
+	}
+	if expiresAt > 0 {
+		c.tokenExpiresAt = time.Unix(expiresAt, 0)
+	}
+}
+
 // SetLog will set/change the output destination.
 // If log file is set paypal will log all requests and responses to this Writer
 func (c *Client) SetLog(log io.Writer) {

types.go

@@ -650,6 +650,8 @@ type (
 		tokenExpiresAt       time.Time
 		returnRepresentation bool
 
+		cache Cache
+
 		// optional rate limiter; if set, SendWithAuth will check it before making requests
 		rateLimiter    limiter.RateLimiter
 		rateLimiterKey string