Can anyone explain this snippet of `ruby`?

Can anyone explain this snippet of `ruby`?

Can any one explain this snippet of ruby ?
def request_phase
service_url = append_params( callback_url, return_url )
[
302,
{
'Location' => login_url( service_url ),
'Content-Type' => 'text/plain'
},
["You are being redirected to CAS for sign-in."]
]
end