- Utilize a Singleton Authenticator:
Ensure that a single instance of your custom Authenticator is used throughout the application.
- Synchronize the authenticate Method:
Add the synchronized keyword to the authenticate method in your custom Authenticator. This ensures that only one thread can execute the method at a time, preventing multiple concurrent token refresh attempts.
- Implement Token Refresh Logic:
Within the synchronized authenticate method, implement the logic to refresh the token if it's expired or invalid. This typically involves making a network call to a token endpoint and obtaining a new token.
- Handle Token Refresh Concurrency:
To prevent multiple threads from attempting to refresh the token simultaneously, use a flag or a Semaphore to indicate that a token refresh is in progress. This ensures that only one thread will attempt to refresh the token at a time.
- Update the Request with the New Token:
Once the token refresh is successful, update the original request with the new token and return the modified request. This allows the request to be retried with the updated token.
- Handle Token Expiration and Renewal:
Implement a mechanism to detect when the token is expiring or has expired. When this occurs, initiate a token refresh and update the token accordingly.
Example Implementation (Kotlin):
class TokenAuthenticator : Authenticator {
private var isRefreshingToken = false
@Synchronized
override fun authenticate(route: Route?, response: Response): Request? {
if (isRefreshingToken) {
// Token refresh is already in progress, return null to avoid concurrent requests
return null
}
isRefreshingToken = true
val newAccessToken = refreshAccessToken() // Make API call to refresh token
isRefreshingToken = false
if (newAccessToken != null) {
// Token refresh successful, update the request with the new token
return response.request.newBuilder()
.header("Authorization", "Bearer $newAccessToken")
.build()
}
// Token refresh failed, return null to indicate that the request should not be retried
return null
}
private fun refreshAccessToken(): String? {
// Make API call to refresh token and return the new token as a string
return null // Placeholder for actual implementation
}
}
Key Points to Consider:
- To ensure thread safety, adding the
synchronized keyword to the
authenticate method is crucial.
- Handle token expiration and renewal to ensure that your application can continue making authenticated requests even when the token expires.
- Implement proper logging and error handling to debug any issues related to token refreshing and authentication.