Improves token manager's refresh token handling

[mdanish98]

Description of Changes

Fixes the issue with retrieving the access token from the refresh token after SSO has reached max.

Related Issue

Closes #530

[aaronzi]

Thank you for the improvements. I added some small remarks.

[aaronzi]

Using System.currentTimeMillis() can be susceptible to system clock changes, which might lead to unexpected behavior.

I would suggest using System.nanoTime() for measuring elapsed time or leverage a time abstraction (e.g., injecting a Clock instance) to make the code more testable and resilient to system clock changes.

[aaronzi]

You are declaring the entire function synchronized for thread safeness. For performance reasons this could be optimized. Here is an example:

public String getAccessToken() throws IOException {
    long currentTimeMillis = System.currentTimeMillis();

    if (accessToken != null && currentTimeMillis < accessTokenExpiryTime) {
        return accessToken;
    }

    synchronized (this) {
        // Re-check within synchronized block
        if (accessToken != null && currentTimeMillis < accessTokenExpiryTime) {
            return accessToken;
        }

        // Proceed with token refresh or retrieval
        // ...
    }
}

[aaronzi]

You have a duplication of logic here for both the refresh and direct retrieval attempts. This could be a possible way of refactoring this. What do you think?

private String refreshAccessToken(long currentTimeMillis) throws IOException {
    return updateTokens(accessTokenProvider.getAccessTokenResponse(tokenEndpoint, refreshToken), currentTimeMillis);
}

private String obtainNewAccessToken(long currentTimeMillis) throws IOException {
    return updateTokens(accessTokenProvider.getAccessTokenResponse(tokenEndpoint), currentTimeMillis);
}

public synchronized String getAccessToken() throws IOException {
    long currentTimeMillis = System.currentTimeMillis();

    if (accessToken != null && currentTimeMillis < accessTokenExpiryTime) {
        return accessToken;
    }

    if (refreshToken != null && currentTimeMillis < refreshTokenExpiryTime) {
        try {
            return refreshAccessToken(currentTimeMillis);
        } catch (IOException e) {
            throw new AccessTokenRetrievalException("Error occurred while refreshing access token", e);
        }
    }

    try {
        return obtainNewAccessToken(currentTimeMillis);
    } catch (IOException e) {
        throw new AccessTokenRetrievalException("Error occurred while obtaining new access token", e);
    }
}

[aaronzi]

LGTM