mongodb 3.0改变了authMechanism

i want try use mongo db with php. If i use mongodb with cli i haven't problem to connection,use and authentication.

But when i use php MongoClient

$db=new MongoClient("mongodb://localhost:27017",array(
"username" => "ehc",
"password" => "pippo"));

$db->selectDB("ehc");
#print_r($db);
$db->close();

i have this error:

Fatal error: Uncaught exception 'MongoConnectionException' with message 'Failed to connect to: localhost:27017: Authentication failed on database 'admin' with username 'ehc': auth failed' in C:\wamp\www\easyhomecosts\server\mongo.php on line 5

The proble is the authMechanism use for user "ehc"

{
  "_id" : "ehc.ehc",
  "user" : "ehc",
  "db" : "ehc",
  "credentials" : {
    "SCRAM-SHA-1" : {
      "iterationCount" : 10000,
      "salt" : "vG26EfcIDTFYq4t2Lki9MA==",
      "storedKey" : "h11Z6bCDtiKAnofqC70FvB9fe7Q=",
      "serverKey" : "pwnXi+Oz6yjXKP2WoJu9bKPRk1c="
    }
  },
  "roles" : [{
      "role" : "dbOwner",
      "db" : "ehc"
    }]
}

I would change the authMechanism for user "ehc" from SCRAM-SHA-1 in MONGODB-CR. after i would change the deafult authMechanism for next users

can you help me?

MONGODB-CR was removed from MongoDB Version 3.0 and only SCRAM-SHA-1 remained. There are many tools and applications that still use MONGODB-CR schema only and there is an workaround for putting it back to a 3.0 instance. Take a look here:
https://jira.mongodb.org/browse/SERVER-17459