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Internal/Membership Authentication

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Keyfiles

x.509
Next Steps

You can require that members of replica sets and sharded clusters authenticate to each other. For the internal authentication of the members, MongoDB can use either keyfiles or x.509 certificates.

The selected method is used for all internal communication. For example, when a client authenticates to a mongos using one of the supported authentication mechanisms, the mongos then uses the configured internal authentication method to connect to the required mongod processes.

Note

Enabling internal authentication also enables client authorization.

Keyfiles

Keyfiles use SCRAM challenge and response authentication mechanism where the keyfiles contain the shared password for the members.

Key Requirements

A key's length must be between 6 and 1024 characters and may only contain characters in the base64 set. MongoDB strips whitespace characters (e.g. x0d, x09, and x20) for cross-platform convenience. As a result, the following operations produce identical keys:

echo -e "mysecretkey" > key1
echo -e "my secret key" > key1
echo -e "my secret key\n" > key2
echo -e "my    secret    key" > key3
echo -e "my\r\nsecret\r\nkey\r\n" > key4

Keyfile Format

Starting in MongoDB 4.2, keyfiles for internal membership authentication use YAML format to allow for multiple keys in a keyfile. The YAML format accepts either:

A single key string (same as in earlier versions)
A sequence of key strings

The YAML format is compatible with the existing single-key keyfiles that use the text file format.

For example,

The ability to specify multiple keys in a file allows for the rolling upgrade of the keys without downtime. See Rotate Keys for Replica Sets and Rotate Keys for Sharded Clusters.

All mongod and mongos instances of a deployment must share at least one common key.

On UNIX systems, the keyfile must not have group or world permissions. On Windows systems, keyfile permissions are not checked.

You must store the keyfile on each server hosting the member of the replica set or sharded clusters.

[1]	For MongoDB's encrypted storage engine, the keyfile used for local key management can only contain a single key .

MongoDB Configuration for Keyfile

To specify the keyfile, use the security.keyFile setting or --keyFile command line option.

For an example of keyfile internal authentication, see Update Replica Set to Keyfile Authentication.

x.509

Members of a replica set or sharded cluster can use x.509 certificates for internal authentication instead of using keyfiles. MongoDB supports x.509 certificate authentication for use with a secure TLS/SSL connection.

Note

MongoDB disables support for TLS 1.0 encryption on systems where TLS 1.1+ is available. For more details, see Disable TLS 1.0.

Member Certificate Requirements

Use member certificates to verify membership to a sharded cluster or a replica set. Member certificate file paths are configured with the net.tls.clusterFile and net.tls.certificateKeyFile options. Members have the following configuration requirements:

Cluster member configuration must specify a non-empty value for at least one of the attributes used for authentication. By default, MongoDB accepts:
- the Organization (O)
- the Organizational Unit (OU)
- the Domain Component (DC)
You can specify alternative attributes to use for authentication by setting net.tls.clusterAuthX509.extensionValue.
Cluster member configuration must include the same net.tls.clusterAuthX509.attributes and use matching values. Attribute order doesn't matter. The following example sets O and OU, but not DC:
```
net:
  tls:
    clusterAuthX509:
      attributes: O=MongoDB, OU=MongoDB Server
```

Note

If you disable the enforceUserClusterSeparation parameter, the following behaviors apply:

The O/OU/DC check is disabled if clusterAuthMode is keyFile in your configuration file. This allows clients possessing member certificates to authenticate as users stored in the $external database.
The server won't start if clusterAuthMode isn't keyFile in your configuration file.

If you set the enforceUserClusterSeparation parameter to false, the server doesn't distinguish between client certificates, which applications use to authenticate, and intra-cluster certificates, which have privileged access. This has no effect if your clusterAuthMode is keyFile. However, if your clusterAuthMode is x509, user certificates that use the allowed scheme are conflated with cluster certificates and granted privileged access.

Your existing certificates are granted internal privileges if you do the following:

Create a user, with a name allowed by this parameter.
Set the enforceUserClusterSeparation parameter to false.
Set clusterAuthMode to x509.

You must not upgrade from keyFile to x509 without validating that you've removed users with elevated privileges that the enforceUserClusterSeparation flag allowed you to create.

To set the enforceUserClusterSeparation parameter to false, run the following command during startup:

mongod --setParameter enforceUserClusterSeparation=false

The certificates have the following requirements:

A single Certificate Authority (CA) must issue all x.509 certificates for the members of a sharded cluster or a replica set.
At least one of the Subject Alternative Name (SAN) entries must match the server hostname used by other cluster members. When comparing SANs, MongoDB can compare either DNS names or IP addresses.
If you don't specify subjectAltName, MongoDB compares the Common Name (CN) instead. However, this usage of CN is deprecated per RFC2818
If the certificate used as the certificateKeyFile includes extendedKeyUsage, the value must include both clientAuth ("TLS Web Client Authentication") and serverAuth ("TLS Web Server Authentication").
```
extendedKeyUsage = clientAuth, serverAuth
```
If the certificate used as the clusterFile includes extendedKeyUsage, the value must include clientAuth.
```
extendedKeyUsage = clientAuth
```

MongoDB Configuration

You can use TLS for internal authentication between each member of your replica set (each mongod instance) or sharded cluster (each mongod and mongos instance).

To use TLS for internal authentication, use the following settings:

security.clusterAuthMode or --clusterAuthMode set to x509
net.tls.clusterFile or --tlsClusterFile (available starting in MongoDB 4.2)

mongod and mongos instances use their certificate key files to prove their identity to clients, but certificate key files can also be used for membership authentication. If you do not specify a cluster file, members use their certificate key files for membership authentication. Specify the certificate key file with net.tls.certificateKeyFile or --tlsCertificateKeyFile (available starting in MongoDB 4.2).

To use the certificate key file for both client authentication and membership authentication, the certificate must either:

Omit extendedKeyUsage or
Specify extendedKeyUsage = serverAuth, clientAuth

Next Steps

For an example of x.509 internal authentication, see Use x.509 Certificate for Membership Authentication.

To upgrade from keyfile internal authentication to x.509 internal authentication, see Upgrade from Keyfile Authentication to x.509 Authentication.

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