By default Mongo is accepting connections without authentication. If, you want to enable authentication, you can add the users to the admin database.

Example: Create a user named root with password test

1. Connect to Mongo
2. Execute command use admin
3. Execute code

     
   db.createUser( 
   { 
   	user: "root", 
   	pwd: "test", 
   	roles: ['clusterAdmin', 'userAdminAnyDatabase', 'readWriteAnyDatabase'] 
   } 
   )
   

4. Start the server with the command bin/mongod --auth
5. Now you can connect with the command bin/mongo -username root -p

You can check the users of current database with the command

• show users

Add user

You can add users to current database with the command
• db.createUser({user:"username",pwd:"password", roles["define the privileges"]})
• remember that you should first select the database (use dbname)

Examples

1. 	db.createUser( 
   	{ user: "testuser_1",
   	  pwd: "testpass",
   	  roles: [ "read" ] 
   	} )
   

2. 	db.createUser( 
   	{ user: "testuser_2",
   	  pwd: "testpass",
   	  roles: [ "readWrite" ] 
   	} )
   

3. 	db.createUser( 
   	{ user: "someAdmin",
       pwd: "verysecretpassword",
   	roles: [ "readWrite","dbAdmin" ] 
   	} )
   

   And if you want to create a admin user which has priveleges to all databases

4. 	use admin	  
   	db.createUser( 
   	{ user: "theAdmin", 
   	  pwd: "verysecretpassword", 
   	  roles: ['clusterAdmin', 'userAdminAnyDatabase', 'readWriteAnyDatabase'] 
   	} )
   

Delete user

You can remove users from the current database with the command
• db.dropUser("username")
You can read more about user roles from http://docs.mongodb.org/manual/reference/user-privileges/