SSL_CTX_set_session_id_context, SSL_set_session_id_context — set context within which session can be reused (server
SSL_CTX_set_session_id_context(SSL_CTX *ctx, const unsigned char
*sid_ctx, unsigned int sid_ctx_len);
*ssl, const unsigned char *sid_ctx, unsigned int sid_ctx_len);
SSL_CTX_set_session_id_context() sets the context sid_ctx
of length sid_ctx_len within which a session can be reused for the
SSL_set_session_id_context() sets the context sid_ctx of length
sid_ctx_len within which a session can be reused for the ssl object.
Sessions are generated within a certain context. When exporting/importing
sessions with i2d_SSL_SESSION/d2i_SSL_SESSION it would be possible,
to re-import a session generated from another context (e.g. another
application), which might lead to malfunctions. Therefore each application
must set its own session id context sid_ctx which is used to distinguish
the contexts and is stored in exported sessions. The sid_ctx can
be any kind of binary data with a given length, it is therefore
possible to use e.g. the name of the application and/or the hostname
and/or service name ...
The session id context becomes part of the session. The session
id context is set by the SSL/TLS server. The SSL_CTX_set_session_id_context()
and SSL_set_session_id_context() functions are therefore only useful
on the server side.
OpenSSL clients will check the session id context returned
by the server when reusing a session.
The maximum length of the sid_ctx is limited to SSL_MAX_SSL_SESSION_ID_LENGTH.
If the session id context is not set on an SSL/TLS server,
stored sessions will not be reused but a fatal error will be flagged
and the handshake will fail.
If a server returns a different session id context to an OpenSSL
client when reusing a session, an error will be flagged and the
handshake will fail. OpenSSL servers will always return the correct
session id context, as an OpenSSL server checks the session id context
itself before reusing a session as described above.
SSL_CTX_set_session_id_context() and SSL_set_session_id_context()
return the following values:
The length sid_ctx_len of the session id context sid_ctx exceeded
the maximum allowed length of SSL_MAX_SSL_SESSION_ID_LENGTH. The
error is logged to the error stack.
The operation succeeded.