How to refresh access token with custom connector (OAuth2)?

Hi v-hashadapu rajendraongole1 
I tried generating new access token from the refresh token but issue with that is i am not able to save the new access token as Credentials so that i can use the new access token instead generating it everytime.
There is no method in power query which saves the new credentials.
Also one more question when the access token or refresh token gets expired it does not ask me for re-authentication. powerbi keeps on using old token.

shared GetValidToken = () =>
    let
        // Fetch the stored credentials from Power BI
        tokens = Extension.CurrentCredential(),
        accessToken = tokens[access_token],
        refreshToken = tokens[refresh_token],
        expiresAtText = tokens[expires],
        // expiration time (text format)
        // Convert expiration time from Text to DateTime
        expiresAt = DateTime.FromText(expiresAtText),
        // Get the current time
        currentTime = DateTime.LocalNow(),
        // Check if the token has expired
        isTokenExpired = expiresAt <= currentTime,

        // If expired, refresh the token
        newTokens =
            if isTokenExpired then
                let
                    // Call the refresh token method to get a new access token
                    refreshedTokens = TokenMethod("refresh_token", refreshToken),
                    // "dan" is placeholder for code_verifier
                    newAccessToken = refreshedTokens[access_token],
                    // New access token
                    newRefreshToken = refreshedTokens[refresh_token],
                    // New refresh token
                    newExpiresAt = refreshedTokens[expires]
                    // New expiration time
                    // Store the new tokens in Power BI credentials
                in
                    Extension.CurrentCredential(
                        [
                            access_token = newAccessToken,
                            refresh_token = newRefreshToken,
                            expires = newExpiresAt
                        ]
                    )
            else
                tokens,
        // Return the existing tokens if not expired
        // Return the valid access token
        validAccessToken = newTokens[access_token]
    in
        validAccessToken;