Unable to authenticate user of firebase using openID

hi guys , i am trying to develop a application in which i used firebase authentication which is easy to implement and i want to save data in the couchbase using sync gateway . i am trying to connect firebase to couchbase base sync gateway using open id . i follow this approch “https://developer.couchbase.com/documentation/mobile/1.4/guides/authentication/openid/index.html” . this i used implecit Flow

my configration json is :

“oidc”: {
“providers”: {
“customfirebase”: {
“issuer”: "my project specific id ",
“client_id”: “google identity toolkit url”,
“register”: true,
“discovery_url”:“my project specific url”,
“validation_key”:"my secret key "




when i pass {db}/_session with token id . i get a error message on console.
" could not verify JWT. Error: oidc: unable to verify JWT signature: no matching keys"
so I am doing right or miss any step.
please help me out