Function refresh 

pub async fn refresh(
    client: &Client,
    base_url: &str,
    client_id: &str,
    current: &TokenSet,
    scope: &str,
    email: &str,
) -> Result<TokenSet, ClientError>

Refresh the access token using the stored refresh token.

Returns the new TokenSet. If Microsoft rotates the refresh token, it’s included in the response and used. If not, the current refresh token is preserved.

Errors:

• ClientError::SessionExpired if Microsoft returns invalid_grant
• ClientError::Graph for other HTTP errors