jlindsey/certify

Automatic client and server certificate distribution and maintenance

Certify

Certify allows easy automatic certificate distribution and maintenance. Certificates are requested as TLS connections are made, courtesy of the GetCertificate and GetClientCertificate tls.Config hooks. Certificates are optionally cached. Simultaneous requests are deduplicated to minimize pressure on issuers.

Users

• Georgetown University

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Issuers

Certify exposes an Issuer interface which is used to allow switching between issuer backends.

Currently implemented issuers:

• Vault PKI Secrets Engine
• Cloudflare CFSSL Certificate Authority
• AWS Certificate Manager Private Certificate Authority

Usage

Create an issuer:

issuer := &vault.Issuer{
    URL: &url.URL{
        Scheme: "https",
        Host: "my-local-vault-instance.com",
    },
    Token:     "myVaultToken",
    Role:      "myVaultRole",
}

Create a Certify:

c := &certify.Certify{
    // Used when request client-side certificates and
    // added to SANs or IPSANs depending on format.
    CommonName: "MyServer.com",
    Issuer: issuer,
    // It is recommended to use a cache.
    Cache: certify.NewMemCache(),
    // It is recommended to set RenewBefore.
    // Refresh cached certificates when < 24H left before expiry.
    RenewBefore: 24*time.Hour,
}

Use in your TLS Config:

tlsConfig := &tls.Config{
    GetCertificate: c.GetCertificate,
}

That's it! Both server-side and client-side certificates can be generated:

tlsConfig := &tls.Config{
    GetClientCertificate: c.GetClientCertificate,
}

For an end-to-end example using gRPC with mutual TLS authentication, see the Vault tests.

How does it work?

Certify hooks into the GetCertificate and GetClientCertificate methods of the Go TLS stack Config struct. These get called when the server/client respectively is required to present its certificate. If possible, this is fetched from the cache, based on the requested server name. If not, a new certificate is issued with the requested server name present. For client requests, the configured CommonName is used.

My presentation at the London HashiCorp meetup has more information:

License