When initialising an SSLContext there is a call to SSL_CTX_set_session_id_context():

#define SID_CTX "Python"
    SSL_CTX_set_session_id_context(self->ctx, (const unsigned char *) SID_CTX,
                                   sizeof(SID_CTX));
#undef SID_CTX

The openssl man pages state that SSL_CTX_set_session_id_context is a "server side only" operation:
https://www.openssl.org/docs/man1.0.2/man3/SSL_CTX_set_session_id_context.html

SSL_CTX_set_session_id_context, SSL_set_session_id_context - set context within which session can be reused (server side only)

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.

In some circumstances, calling this on a client side socket can result in unexpected behavior. For example TLSv1.3 PSK: #103181 (comment)

The fix for this was originally part of another PR (#103181) @gpshead recommended creating a separate issue/PR

Linked PRs

• gh-105293: Do not call SSL_CTX_set_session_id_context on client side SSL context #105295