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 :
{
“interface”:":4981",
“adminInterface”:":4982",
“log”:["*"],

“databases”:{
“sample”:{
“server”:“http://localhost:8091”,
“bucket”:“sample”,
“oidc”: {
“providers”: {
“customfirebase”: {
“issuer”: "my project specific id ",
“client_id”: “google identity toolkit url”,
“disable_cfg_validation”:true,
“register”: true,
“discovery_url”:“my project specific url”,
“user_prefix”:“firebase_”,
“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