feat(go-sdk): Automatically refresh expired authentication tokens (#1608)

The Looker Go SDK was not automatically refreshing expired
authentication tokens, causing authentication to fail after one hour.
This change modifies the AuthSession to proactively manage the token's
lifecycle. An IsActive method was added to check the token's validity,
and a Login method was added to refresh the token when needed. The Do
method was updated to call Login before making any API requests,
ensuring the token is always active.


Fixes #1606 🦕

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: drstrangelooker

go/rtl/auth.go

@@ -10,6 +10,7 @@ import (
 	"net/url"
 	"os"
 	"reflect"
+	"sync"
 	"time"
 
 	"golang.org/x/oauth2"
@@ -39,6 +40,47 @@ func (t *transportWithHeaders) RoundTrip(req *http.Request) (*http.Response, err
 type AuthSession struct {
 	Config ApiSettings
 	Client http.Client
+	token  *oauth2.Token
+	source oauth2.TokenSource
+	mu     sync.RWMutex
+}
+
+const tokenLeeway = 10 * time.Second
+
+func (s *AuthSession) IsActive() bool {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	if s.token == nil {
+		return false
+	}
+	return s.token.Expiry.After(time.Now().Add(tokenLeeway))
+}
+
+func (s *AuthSession) Login() (*oauth2.Token, error) {
+	// First, check with a read lock to avoid contention if the token is valid.
+	s.mu.RLock()
+	if s.token != nil && s.token.Expiry.After(time.Now().Add(tokenLeeway)) {
+		token := s.token
+		s.mu.RUnlock()
+		return token, nil
+	}
+	s.mu.RUnlock()
+
+	// If the token is invalid or nil, acquire a write lock to refresh it.
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	// Re-check after obtaining the write lock, in case another goroutine refreshed it.
+	if s.token != nil && s.token.Expiry.After(time.Now().Add(tokenLeeway)) {
+		return s.token, nil
+	}
+
+	token, err := s.source.Token()
+	if err != nil {
+		return nil, err
+	}
+	s.token = token
+	return token, nil
 }
 
 func NewAuthSession(config ApiSettings) *AuthSession {
@@ -74,21 +116,27 @@ func NewAuthSessionWithTransport(config ApiSettings, transport http.RoundTripper
 		&http.Client{Transport: appIdHeaderTransport},
 	)
 
+	source := oauthConfig.TokenSource(ctx)
+
 	// Make use of oauth2 transport to handle token management
 	oauthTransport := &oauth2.Transport{
-		Source: oauthConfig.TokenSource(ctx),
+		Source: source,
 		// Will set "x-looker-appid" Header on all other requests
 		Base: appIdHeaderTransport,
 	}
 
 	return &AuthSession{
 		Config: config,
 		Client: http.Client{Transport: oauthTransport},
+		source: source,
 	}
 }
 
 func (s *AuthSession) Do(result interface{}, method, ver, path string, reqPars map[string]interface{}, body interface{}, options *ApiSettings) error {
-
+	_, err := s.Login()
+	if err != nil {
+		return err
+	}
 	// prepare URL
 	u := fmt.Sprintf("%s/api%s%s", s.Config.BaseUrl, ver, path)