How to Efficiently Refresh Google API Client Access Tokens to Avoid 'invalid_grant' Errors?

Refreshing Google API Client Access Tokens

Understanding the Issue

When using the Google Analytics API, you may encounter errors when trying to access data from multiple Google Accounts. This issue arises because access tokens expire after an hour. Refreshing the token using $client->refreshToken() should resolve the problem, but in some cases, it may return an "invalid_grant" error.

Solution

To correctly refresh the token, you need to understand the following:

• First Token: The initial token you obtain during authentication includes a refresh token.
• Temp Token: The refreshed token, obtained using $client->refreshToken($refreshToken), is valid for an hour.
• Refresh Time: Both the first token and the temp token expire after an hour.

Code Implementation

The attached code demonstrates a solution for managing token expiration:

// Retrieve the original token.
$originalToken = json_decode($token);

// Calculate token expiration time.
$now = time();
$expirationTime = $originalToken->created + 3600;

// Check if token is expired.
if ($now > $expirationTime) {
    // If expired, use the refresh token from the original token to obtain a new temporary token.
    $client->refreshToken($originalToken->refresh_token);
    $newToken = $client->getAccessToken();
    $tokenQuery = "UPDATE token SET token='$newToken' WHERE type='refresh'";
    mysqli_query($cxn, $tokenQuery);
    $token = $newToken;
} else {
    // If the original token hasn't expired, set the token as the original token.
    $client->setAccessToken($token);
}

This code retrieves the original token, calculates its expiration time, and checks if it has expired. If so, it refreshes the token using the refresh token and updates the database. If the original token hasn't expired, it sets the client's access token as the original token.

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