Icorrect encoding of request body in plugins.api.API.login

[crazyscientist]

The body for the login request is constructed like this:

        const body = `username=${username}&password=${password}`;
        const response = await this._fetch({
            url: url,
            method: 'POST',
            body: encodeURI(body),
            headers: {'Content-Type': 'application/x-www-form-urlencoded'}
        });

This is incorrect and prevents users from logging in, if the password starts with a $.