OAuth 1, wrong OAuth redirect
Hi !

I'm trying to use grant with Sellsy (https://go.sellsy.com/fr/).

Here is my configuration:

```js
{
    sellsy: {
      enabled: true,
      request_url: "https://apifeed.sellsy.com/0/request_token",
      authorize_url: "https://apifeed.sellsy.com/0/oauth/access_token",
      access_url: "https://apifeed.sellsy.com/0/login.php?",
      oauth: 1,
      key: "XXX",
      secret: "XXX",
      callback: "http://localhost:1337/auth/sellsy/callback",
    }
}
```

The problem is that the url where grant redirects the user is:
http://localhost:1337/connect/authentification_url=https://apifeed.sellsy.com/0/login.php&oauth_token=0a1bfe71494c3fe920c2adfd9bb5853dc2d1f&oauth_token_secret=395dsqfqfdff8daae8de6da5879ed053&oauth_callback_confirmed=true

It doesn't work but if I remove the first part ('http://localhost:1337/connect/authentification_url=') and if I replace the '&' after login.php with an '?' the redirection works.

What am I missing with the configuration?

Thanks a lot

