This guide shows you how to enable authentication in MongoDB. The authentication is disabled by default. To configure it, you must first add a user to the “admin” database.

> show dbs
admin  #add single user to this database
testdb

P.S This example is using MongoDB version 2.2.3

Authentication example

See a full example to add a “admin” user to the admin database, and a normal user to the “testdb” database, and how to perform the authentication.

$mongo --auth

$ mongo
MongoDB shell version: 2.2.3
connecting to: test
> use admin             		#1. connect to the "admin" database.
switched to db admin			
> db.addUser("admin","password")	#2. add a user "admin" to the admin database. 
	"user" : "admin",
	"readOnly" : false,
	"pwd" : "90f500568434c37b61c8c1ce05fdf3ae",
	"_id" : ObjectId("513af8cac115e7a6b4bcceb9")
addUser succeeded, but cannot wait for replication since we no longer have auth
> use testdb				#3. connect to the "testdb" database.
switched to db testdb
> show collections			#4. now, read and write need authentication
Sat Mar  9 16:54:57 uncaught exception: error: {
	"$err" : "unauthorized db:testdb ns:testdb.system.namespaces lock type:0 client:127.0.0.1",
	"code" : 10057
> use admin				#5. connect back to the "admin" database.
switched to db admin
> db.auth("admin","password")		#6. performs authentication, 1 means succeed, 0 means failed
> use testdb				#7. connect to the "testdb" database.
switched to db testdb
> show collections			#8. no problem, it shows all collections
system.indexes
user
> db.addUser("testdb","password")       #9. add another user "testdb" to the "testdb" database.
	"user" : "testdb",
	"readOnly" : false,
	"pwd" : "b9ff75cbf18bd98d8554efec12c72090",
	"_id" : ObjectId("513af934c115e7a6b4bcceba")
> show collections
system.indexes
system.users				#10. All users' data are stored in this system.users collection.
user
> db.system.users.find()
{ "_id" : ObjectId("513af934c115e7a6b4bcceba"), "user" : "testdb", "readOnly" : false, "pwd" : "b9ff75cbf18bd98d8554efec12c72090" }
>

Done.

References

1. MongoDB : Security Practices and Management
2. Java MongoDB authentication example