Fixed the Oauth token expiring issue (#2)

* Fixed the Oauth token expiring issue
Added the logic for refreshing the token manually when there's only a minute left till expiration
Added a mutex lock for the code of fetching the token from database to handle concurrency issues

* Removed some useless code and fixed a comment

* Review fixes

* Update server/plugin.go

Co-authored-by: shivamjosh <85667960+shivamjosh@users.noreply.github.com>

Co-authored-by: shivamjosh <85667960+shivamjosh@users.noreply.github.com>

server/plugin.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/mattermost/mattermost-server/v5/model"
 	"github.com/mattermost/mattermost-server/v5/plugin"
@@ -47,6 +48,7 @@ type Plugin struct {
 
 	// configurationLock synchronizes access to the configuration.
 	configurationLock sync.RWMutex
+	tokenLock         sync.Mutex
 
 	// configuration is the active plugin configuration. Consult getConfiguration and
 	// setConfiguration for usage.
@@ -196,6 +198,8 @@ func (p *Plugin) getGitlabUserInfoByMattermostID(userID string) (*gitlab.UserInf
 
 	var userInfo gitlab.UserInfo
 
+	p.tokenLock.Lock()
+	defer p.tokenLock.Unlock()
 	if infoBytes, err := p.API.KVGet(userID + GitlabTokenKey); err != nil || infoBytes == nil {
 		return nil, &APIErrorResponse{ID: APIErrorIDNotConnected, Message: "Must connect user account to GitLab first.", StatusCode: http.StatusBadRequest}
 	} else if err := json.Unmarshal(infoBytes, &userInfo); err != nil {
@@ -209,6 +213,19 @@ func (p *Plugin) getGitlabUserInfoByMattermostID(userID string) (*gitlab.UserInf
 	}
 
 	userInfo.Token.AccessToken = unencryptedToken
+	newToken, err := p.checkAndRefreshToken(userInfo.Token)
+	if err != nil {
+		return nil, &APIErrorResponse{ID: "", Message: err.Error(), StatusCode: http.StatusInternalServerError}
+	}
+
+	if newToken != nil {
+		userInfo.Token = newToken
+		unencryptedToken = newToken.AccessToken // needed because the storeGitlabUserInfo method changes its value to an encrypted value
+		if err := p.storeGitlabUserInfo(&userInfo); err != nil {
+			return nil, &APIErrorResponse{ID: "", Message: fmt.Sprintf("Unable to store user info. Error: %s", err.Error()), StatusCode: http.StatusInternalServerError}
+		}
+		userInfo.Token.AccessToken = unencryptedToken
+	}
 
 	return &userInfo, nil
 }
@@ -491,3 +508,23 @@ func (p *Plugin) HasGroupHook(user *gitlab.UserInfo, namespace string) (bool, er
 
 	return found, err
 }
+
+func (p *Plugin) checkAndRefreshToken(token *oauth2.Token) (*oauth2.Token, error) {
+	// If there is only one minute left for the token to expire, we are refreshing the token.
+	// The detailed reason for this can be found here: https://github.com/golang/oauth2/issues/84#issuecomment-831492464
+	// We don't want the token to expire between the time when we decide that the old token is valid
+	// and the time at which we create the request. We are handling that by not letting the token expire.
+	if time.Until(token.Expiry) <= 1*time.Minute {
+		conf := p.getOAuthConfig()
+		src := conf.TokenSource(context.Background(), token)
+		newToken, err := src.Token() // this actually goes and renews the tokens
+		if err != nil {
+			return nil, errors.Wrap(err, "unable to get the new refreshed token")
+		}
+		if newToken.AccessToken != token.AccessToken {
+			return newToken, nil
+		}
+	}
+
+	return nil, nil
+}