EEL

example_login

event login {
    has $session-id = #post.req-id;
    has $timestamp  = #post.timestamp;
    match {
        request(#get , method == "GET" , path == "/login", status == 200)
        request(#post, method == "POST", path == "/login", status == 200, req-id == #get.req-id)
    }
}

running

raku -I. -MEEL -e '
my Supplier $supplier .= new;
eel($supplier.Supply, :code("examples/login")).tap: *.say; 

$supplier.emit: %( :type<request>, :method<GET> , :path</>,      :req-id<aaaa1111>, :status(200)                      );
$supplier.emit: %( :type<request>, :method<GET> , :path</>,      :req-id<aaaa2222>, :status(200)                      );
$supplier.emit: %( :type<request>, :method<GET> , :path</login>, :req-id<1234abcd>, :status(200)                      );
$supplier.emit: %( :type<request>, :method<GET> , :path</>,      :req-id<aaaa3333>, :status(200)                      );
$supplier.emit: %( :type<request>, :method<GET> , :path</login>, :req-id<4321xyzz>, :status(200)                      );
$supplier.emit: %( :type<request>, :method<POST>, :path</login>, :req-id<1234abcd>, :status(200), :session-id<abc123> );

'
{session-id => abc123, timestamp => Instant:1581984202.052599, type => login}