add_certificate

        # OpenSSL::SSL::SSLContext.add_certificate

(from ruby core)
### Implementation from SSLContext
---
    ctx.add_certificate(certificate, pkey [, extra_certs]) -> self

---

Adds a certificate to the context. *pkey* must be a corresponding
private key with *certificate*.

Multiple certificates with different public key type can be added by
repeated calls of this method, and OpenSSL will choose the most
appropriate certificate during the handshake.

#cert=, #key=, and #extra_chain_cert= are old accessor methods for
setting certificate and internally call this method.

### Parameters
*certificate*
:   A certificate. An instance of OpenSSL::X509::Certificate.
*pkey*
:   The private key for *certificate*. An instance of
    OpenSSL::PKey::PKey.
*extra_certs*
:   Optional. An array of OpenSSL::X509::Certificate. When sending a
    certificate chain, the certificates specified by this are sent
    following *certificate*, in the order in the array.


### Example
    rsa_cert = OpenSSL::X509::Certificate.new(...)
    rsa_pkey = OpenSSL::PKey.read(...)
    ca_intermediate_cert = OpenSSL::X509::Certificate.new(...)
    ctx.add_certificate(rsa_cert, rsa_pkey, [ca_intermediate_cert])

    ecdsa_cert = ...
    ecdsa_pkey = ...
    another_ca_cert = ...
    ctx.add_certificate(ecdsa_cert, ecdsa_pkey, [another_ca_cert])