Issue with Edgeryders form

A separate question for @matthias about the multisite_account_api_key.json endpoint.

If I call this once the user has logged in via SSO, what is the payload?

Currently I am following the manual:

https://communities.edgeryders.eu/multisite_account_api_key.json?hostname=edgeryders.eu

But the manual also suggests a session cookie is required, is this then passed in a url parameter to get the user API key?

A cookie is set on redirect after SSO login, it looks like this:

redirect=YWRtaW49ZmFsc2UmbW9kZXJhdG9yPWZhbHNlJmF2YXRhcl91cmw9aHR0cHMlM0ElMkYlMkZjb21tdW5pdGllcy5lZGdlcnlkZXJzLmV1JTJGdXBsb2FkcyUyRmNvbW11bml0aWVzJTJGb3JpZ2luYWwlMkYyWCUyRmMlMkZjYTk5ZmE3ZmZiMGIxZDNiNDE3NDgyNjFlZWQ4ZjY2NzY1NmUyNjk3LmpwZyZlbWFpbD1vd2VuZ290JTQwZ21haWwuY29tJmV4dGVybmFsX2lkPTQwNjcmZ3JvdXBzPXRydXN0X2xldmVsXzAlMkN0cnVzdF9sZXZlbF8xJTJDdHJ1c3RfbGV2ZWxfMiZub25jZT0xMjM0JnJldHVybl9zc29fdXJsPWh0dHAlM0ElMkYlMkZsb2NhbGhvc3QlM0E4MDgwJTJGJnVzZXJuYW1lPW93ZW4=

Need a bit more on this part to get it working.