ssl:ssl_add_certificate

ssl_add_certificate_key(+SSL0, +Certificate, +Key, -SSL): Add an additional certificate/key pair to SSL0, yielding SSL. Certificate and Key are either strings or atoms that hold the PEM-encoded certificate plus certificate chain and private key, respectively. Using strings is preferred for security reasons.
This predicate allows dual-stack RSA and ECDSA servers (for example), and is an alternative for using the certificate_key_pairs/1 option. As of OpenSSL 1.0.2, multiple certificate types with completely independent certificate chains are supported. If a certificate of the same type is added repeatedly to a context, the result is undefined. Currently, up to 12 additional certificates of different types are admissible.