Configuring TLS

Configuration with URI options

Enable TLS by including tls=true in the URI.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/");
mongoc_uri_set_option_as_bool (uri, MONGOC_URI_TLS, true);

mongoc_client_t *client = mongoc_client_new_from_uri (uri);

The following URI options may be used to further configure TLS:

Constant	Key	Description
MONGOC_URI_TLS	tls	{true|false}, indicating if TLS must be used.
MONGOC_URI_TLSCERTIFICATEKEYFILE	tlscertificatekeyfile	Path to PEM formatted Private Key, with its Public Certificate concatenated at the end.
MONGOC_URI_TLSCERTIFICATEKEYFILEPASSWORD	tlscertificatekeypassword	The password, if any, to use to unlock encrypted Private Key.
MONGOC_URI_TLSCAFILE	tlscafile	One, or a bundle of, Certificate Authorities whom should be considered to be trusted.
MONGOC_URI_TLSALLOWINVALIDCERTIFICATES	tlsallowinvalidcertificates	Accept and ignore certificate verification errors (e.g. untrusted issuer, expired, etc.)
MONGOC_URI_TLSALLOWINVALIDHOSTNAMES	tlsallowinvalidhostnames	Ignore hostname verification of the certificate (e.g. Man In The Middle, using valid certificate, but issued for another hostname)
MONGOC_URI_TLSINSECURE	tlsinsecure	{true|false}, indicating if insecure TLS options should be used. Currently this implies MONGOC_URI_TLSALLOWINVALIDCERTIFICATES and MONGOC_URI_TLSALLOWINVALIDHOSTNAMES.
MONGOC_URI_TLSDISABLECERTIFICATEREVOCATIONCHECK	tlsdisablecertificaterevocationcheck	{true|false}, indicates if revocation checking (CRL / OCSP) should be disabled.
MONGOC_URI_TLSDISABLEOCSPENDPOINTCHECK	tlsdisableocspendpointcheck	{true|false}, indicates if OCSP responder endpoints should not be requested when an OCSP response is not stapled.

Configuration with mongoc_ssl_opt_t

Alternatively, the mongoc_ssl_opt_t struct may be used to configure TLS with mongoc_client_set_ssl_opts() or mongoc_client_pool_set_ssl_opts(). Most of the configurable options can be set using the Connection String URI.

mongoc_ssl_opt_t key	URI key
pem_file	tlsClientCertificateKeyFile
pem_pwd	tlsClientCertificateKeyPassword
ca_file	tlsCAFile
weak_cert_validation	tlsAllowInvalidCertificates
allow_invalid_hostname	tlsAllowInvalidHostnames

The only exclusions are crl_file and ca_dir. Those may only be set with mongoc_ssl_opt_t.

Client Authentication

When MongoDB is started with TLS enabled, it will by default require the client to provide a client certificate issued by a certificate authority specified by --tlsCAFile, or an authority trusted by the native certificate store in use on the server.

To provide the client certificate, set the tlsCertificateKeyFile in the URI to a PEM armored certificate file.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/");
mongoc_uri_set_option_as_bool (uri, MONGOC_URI_TLS, true);
mongoc_uri_set_option_as_utf8 (uri, MONGOC_URI_TLSCERTIFICATEKEYFILE, "/path/to/client-certificate.pem");

mongoc_client_t *client = mongoc_client_new_from_uri (uri);

Server Certificate Verification

The MongoDB C Driver will automatically verify the validity of the server certificate, such as issued by configured Certificate Authority, hostname validation, and expiration.

To overwrite this behavior, it is possible to disable hostname validation, OCSP endpoint revocation checking, revocation checking entirely, and allow invalid certificates.

This behavior is controlled using the tlsAllowInvalidHostnames, tlsDisableOCSPEndpointCheck, tlsDisableCertificateRevocationCheck, and tlsAllowInvalidCertificates options respectively. By default, all are set to false.

It is not recommended to change these defaults as it exposes the client to Man In The Middle attacks (when tlsAllowInvalidHostnames is set), invalid certificates (when tlsAllowInvalidCertificates is set), or potentially revoked certificates (when tlsDisableOCSPEndpointCheck or tlsDisableCertificateRevocationCheck are set).

Supported Libraries

By default, libmongoc will attempt to find a supported TLS library and enable TLS support. This is controlled by the cmake flag ENABLE_SSL, which is set to AUTO by default. Valid values are:

• AUTO the default behavior. Link to the system’s native TLS library, or attempt to find OpenSSL.

• DARWIN link to Secure Transport, the native TLS library on macOS.

• WINDOWS link to Secure Channel, the native TLS library on Windows.

• OPENSSL link to OpenSSL (libssl). An optional install path may be specified with OPENSSL_ROOT.

• LIBRESSL link to LibreSSL’s libtls. (LibreSSL’s compatible libssl may be linked to by setting OPENSSL).

• OFF disable TLS support.

OpenSSL

The MongoDB C Driver uses OpenSSL, if available, on Linux and Unix platforms (besides macOS). Industry best practices and some regulations require the use of TLS 1.1 or newer, which requires at least OpenSSL 1.0.1. Check your OpenSSL version like so:

$ openssl version

Ensure your system’s OpenSSL is a recent version (at least 1.0.1), or install a recent version in a non-system path and build against it with:

cmake -DOPENSSL_ROOT_DIR=/absolute/path/to/openssl

When compiled against OpenSSL, the driver will attempt to load the system default certificate store, as configured by the distribution. That can be overridden by setting the tlsCAFile URI option or with the fields ca_file and ca_dir in the mongoc_ssl_opt_t.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is fully supported when using OpenSSL 1.0.1+ with the following notes:

• When a crl_file is set with mongoc_ssl_opt_t, and the crl_file revokes the server’s certificate, the certificate is considered revoked (even if the certificate has a valid stapled OCSP response)

LibreSSL / libtls

The MongoDB C Driver supports LibreSSL through the use of OpenSSL compatibility checks when configured to compile against openssl. It also supports the new libtls library when configured to build against libressl.

When compiled against the Windows native libraries, the crl_file option of a mongoc_ssl_opt_t is not supported, and will issue an error if used.

Setting tlsDisableOCSPEndpointCheck and tlsDisableCertificateRevocationCheck has no effect.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with the following notes:

• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a Must-Staple certificate is presented with no stapled response (unless the client receives a revoked response from an OCSP responder).

• Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down.

Native TLS Support on Windows (Secure Channel)

The MongoDB C Driver supports the Windows native TLS library (Secure Channel, or SChannel), and its native crypto library (Cryptography API: Next Generation, or CNG).

When compiled against the Windows native libraries, the ca_dir option of a mongoc_ssl_opt_t is not supported, and will issue an error if used.

Encrypted PEM files (e.g., setting tlsCertificateKeyPassword) are also not supported, and will result in error when attempting to load them.

When tlsCAFile is set, the driver will only allow server certificates issued by the authority (or authorities) provided. When no tlsCAFile is set, the driver will look up the Certificate Authority using the System Local Machine Root certificate store to confirm the provided certificate.

When crl_file is set with mongoc_ssl_opt_t, the driver will import the revocation list to the System Local Machine Root certificate store.

Setting tlsDisableOCSPEndpointCheck has no effect.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with the following notes:

• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a Must-Staple certificate is presented with no stapled response (unless the client receives a revoked response from an OCSP responder).

• When a crl_file is set with mongoc_ssl_opt_t, and the crl_file revokes the server’s certificate, the OCSP response takes precedence. E.g. if the server presents a certificate with a valid stapled OCSP response, the certificate is considered valid even if the crl_file marks it as revoked.

• Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down.

Native TLS Support on macOS / Darwin (Secure Transport)

The MongoDB C Driver supports the Darwin (OS X, macOS, iOS, etc.) native TLS library (Secure Transport), and its native crypto library (Common Crypto, or CC).

When compiled against Secure Transport, the ca_dir and crl_file options of a mongoc_ssl_opt_t are not supported. An error is issued if either are used.

When tlsCAFile is set, the driver will only allow server certificates issued by the authority (or authorities) provided. When no tlsCAFile is set, the driver will use the Certificate Authorities in the currently unlocked keychains.

Setting tlsDisableOCSPEndpointCheck and tlsDisableCertificateRevocationCheck has no effect.

The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with the following notes.

• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a Must-Staple certificate is presented with no stapled response (unless the client receives a revoked response from an OCSP responder).

• Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down.