GitLab

pt-spec.txt:

      "TOR_PT_SERVER_TRANSPORT_OPTIONS" -- A semicolon-separated list
       of <key>:<value> pairs, where <key> is a transport name and
       <value> is a k=v string value with options that are to be passed
       to the transport. Colons, semicolons, equal signs and backslashes
       MUST be escaped with a backslash. TOR_PT_SERVER_TRANSPORT_OPTIONS
       is optional and might not be present in the environment of the
       proxy if no options are need to be passed to transports.

or/transports.c:get_transport_options_for_server_proxy()

      char *escaped_opts = tor_escape_str_for_pt_args(options, ":;\\");

Equal signs are not escaped. I'm not sure if anything will break with different behavior.