not able to add proper rule for firebase custom claim - ruby-on-rails

Question

I have created an auth token using Firebase documentation for ruby but then when I am trying to access the custom claim in the data security rules it does not work.
my JWT creation code looks something like this
$service_account_email = "service-account#my-project-abc123.iam.gserviceaccount.com"
$private_key = OpenSSL::PKey::RSA.new "-----BEGIN PRIVATE KEY-----\n..."
now_seconds = Time.now.to_i
payload = {:iss => $service_account_email,
:sub => $service_account_email,
:aud => "https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit",
:iat => now_seconds,
:exp => now_seconds+(60*60), # Maximum expiration time is one hour
:uid => uid,
:claims => {:modify_vessels => true}}
jwt_token = JWT.encode payload, private_key, "RS256"
render json: { :status => "ok", :email => usr, :jwt_token => jwt_token, :uid => uid } and return
I have tried below rules for accessing claims object but none of them work
{
"rules": {
"vessels" : {
"$uid" : {
".read":"auth.token.modify_vessels === true",
".write":"auth.token.modify_vessels === true"
}
}
}
}
and
{
"rules": {
"vessels" : {
"$uid" : {
".read":"auth.claims.modify_vessels === true",
".write":"auth.claims.modify_vessels === true"
}
}
}
}
Please Note :- I can do auth.uid and it works
Any help on this will be helpful