> db
mydb
> db.getUsers()
[
    {
        "_id"  : "mydb.mongo",
        "user" : "mongo",
        "db"   : "mydb",
        "roles" : [
            {
            "role" : "dbOwner",
            "db" : "mydb"
            }
        ],
        "mechanisms" : [
            "SCRAM-SHA-1",
            "SCRAM-SHA-256"
        ]
    }
]


 > db.changeUserPassword("mongo", "mongo_n3w_p4ss");
2019-05-22T20:58:10.128-0500 E QUERY    [thread1] Error: Updating user failed: Use of SCRAM-SHA-256 requires undigested passwords :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
DB.prototype.updateUser@src/mongo/shell/db.js:1487:15
DB.prototype.changeUserPassword@src/mongo/shell/db.js:1491:9
@(shell):1:1
> db.version()
4.0.5