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MongoDB supports x.509 certificate authentication for client authentication and internal authentication of the members of replica sets and sharded clusters.

x.509 certificate authentication requires a secure TLS/SSL connection.


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

Certificate Authority

For production use, your MongoDB deployment should use valid certificates generated and signed by a certificate authority. You or your organization can generate and maintain an independent certificate authority, or use certificates generated by third-party TLS/SSL vendors. Obtaining and managing certificates is beyond the scope of this documentation.

Client x.509 Certificates

To authenticate to servers, clients can use x.509 certificates instead of usernames and passwords.

Client Certificate Requirements

The client certificate must have the following properties:

  • A single Certificate Authority (CA) must issue the certificates for both the client and the server.

  • Client certificates must contain the following fields:

    keyUsage = digitalSignature
    extendedKeyUsage = clientAuth
  • Each unique MongoDB user must have a unique certificate.

  • The subject of a client x.509 certificate, which contains the Distinguished Name (DN), must be different than the subjects of member x.509 certificates.


    If a client x.509 certificate’s subject matches the O, OU, and DC attributes of the Member x.509 Certificate (or tlsX509ClusterAuthDNOverride, if set) exactly, the client connection is accepted, full permissions are granted, and a warning message appears in the log.

    Only cluster member x509 certificates should use the same O, OU, and DC attribute combinations.

    New in version 4.2: If the MongoDB deployment has tlsX509ClusterAuthDNOverride set, the client x.509 certificate’s subject must not match that value.


    If a client x.509 certificate’s subject has the same O, OU, and DC combination as the Member x.509 Certificate (or tlsX509ClusterAuthDNOverride if set), the client connection is rejected. Only cluster member x509 certificates should use the same O, OU, and DC combinations as this grants full permissions.

MongoDB User and $external Database

To authenticate with a client certificate, you must first add the value of the subject from the client certificate as a MongoDB user. Each unique x.509 client certificate corresponds to a single MongoDB user; i.e. you cannot use a single client certificate to authenticate more than one MongoDB user.

Add the user in the $external database; i.e. the Authentication Database is the $external database

Changed in version 3.6.3: To use sessions with $external authentication users (i.e. Kerberos, LDAP, x.509 users), the usernames cannot be greater than 10k bytes.


To connect and authenticate using x.509 client certificate:

You can also make the TLS/SSL connection first, and then use db.auth() in the $external database to authenticate.

For examples of both cases, see the Authenticate with a x.509 Certificate (Using tls Options) section in Use x.509 Certificates to Authenticate Clients

TLS Connection X509 Certificate Startup Warning

Starting in MongoDB 4.2.15, mongod and mongos now issue a startup warning when their certificates do not include a Subject Alternative Name attribute.

The following platforms do not support common name validation:

  • iOS 13 and higher
  • MacOS 10.15 and higher
  • Go 1.15 and higher

Clients using these platforms will not authenticate to MongoDB servers which use X.509 certificate whose hostnames are specified by CommonName attributes.

Member x.509 Certificates

For internal authentication, members of sharded clusters and replica sets can use x.509 certificates instead of keyfiles, which use the SCRAM authentication mechanism.

Member Certificate Requirements

The member certificate (net.tls.clusterFile, if specified, and net.tls.certificateKeyFile), used to verify membership to the sharded cluster or a replica set, must have the following properties:

  • A single Certificate Authority (CA) must issue all the x.509 certificates for the members of a sharded cluster or a replica set.

  • The Distinguished Name (DN), found in the member certificate’s subject, must specify a non-empty value for at least one of the following attributes: Organization (O), the Organizational Unit (OU) or the Domain Component (DC).

  • The Organization attributes (O’s), the Organizational Unit attributes (OU’s), and the Domain Components (DC’s) must match those from both the net.tls.clusterFile and net.tls.certificateKeyFile certificates for the other cluster members (or the tlsX509ClusterAuthDNOverride value, if set).

    To match, the certificate must match all specifications of these attributes, or even the non-specification of these attributes. The order of the attributes does not matter.

    In the following example, the two DN’s contain matching specifications for O, OU as well as the non-specification of the DC attribute.

    C=US, ST=CA, O=MongoDB, OU=Dept1, CN=host2

    However, the following two DN’s contain a mismatch for the OU attribute since one contains two OU specifications and the other, only one specification.

  • Either the Common Name (CN) or one of the Subject Alternative Name (SAN) entries must match the server hostname for other cluster members. Starting in MongoDB 4.2, when comparing SANs, MongoDB can compare either DNS names or IP addresses. In previous versions, MongoDB only compares DNS names.

    For example, the certificates for a cluster could have the following subjects:

    subject= CN=<myhostname1>,OU=Dept1,O=MongoDB,ST=NY,C=US
    subject= CN=<myhostname2>,OU=Dept1,O=MongoDB,ST=NY,C=US
    subject= CN=<myhostname3>,OU=Dept1,O=MongoDB,ST=NY,C=US
  • If the certificate includes the Extended Key Usage (extendedKeyUsage) setting, the value must include clientAuth (“TLS Web Client Authentication”).

    extendedKeyUsage = clientAuth

    You can also use a certificate that does not include the Extended Key Usage (EKU).

MongoDB Configuration for Membership Authentication

In addition to any TLS/SSL configurations as appropriate for your deployment, include the following to specify x.509 for internal authentication for each member of your replica set (i.e. the mongod instances) or sharded cluster (i.e. the mongod and mongos instances):

However, if no cluster file is specified, members can use their certificate key file specified in net.tls.certificateKeyFile or --tlsCertificateKeyFile (both new in MongoDB 4.2) for membership authentication. This certificate key file is used by mongod (and mongos) instances to prove their identity to clients, but can also be used for membership authentication. To use for both client authentication and membership authentication, the certificate must either:

  • Omit extendedKeyUsage or
  • Specify extendedKeyUsage values


Athough still available, net.ssl.clusterFile (and the correponding --sslClusterFile) and net.ssl.PEMKeyFile (and the corresponding --sslPEMKeyFile) are deprecated as of MongoDB 4.2.

For deployments using MongoDB version 4.0 and earlier, use net.ssl.clusterFile (or the corresponding --sslClusterFile) and net.ssl.PEMKeyFile (or the corresponding --sslPEMKeyFile).

Next Steps

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