Add WAMP message internal-only attributes for publisher/caller disclosure

[oberstet]

from https://crossbario.slack.com/archives/C0473JCQ6/p1591287619078900

would work like this:

• sessions embedded inside the router worker (such as rlinks) are using https://github.com/crossbario/crossbar/blob/7a24af99fce6d057c63a9c7b144b0418ca627f4e/crossbar/router/session.py#L69
• such session received WAMP messages here https://github.com/crossbario/crossbar/blob/master/crossbar/router/session.py#L273
• so the event handler in rlink gets a native python WAMP msg object (without previous serialization/deserialization)
• so we could just stick the publisher session ID/authid/authrole into a non-serialized attribute here https://github.com/crossbario/autobahn-python/blob/master/autobahn/wamp/message.py#L3141 ..
• .. and omit this internal-use-only attribute in

  autobahn-python/autobahn/wamp/message.py

  Line 3742 in effc130

  def marshal(self):

IOW, like:

Event._internal_only_publisher
Event._internal_only_publisher_authid
Event._internal_only_publisher_authrole
Call._internal_only_caller
Call._internal_only_caller_authid
Call._internal_only_caller_authrole

we can probably do that generically, for any WAMP message sent/received in Message https://github.com/crossbario/autobahn-python/blob/master/autobahn/wamp/message.py#L362

[oberstet]

background:

• rlinks (for router-to-router) need to have the original publisher/caller to fill in forward_for
• since rlinks sit as regular, but router-embedded sessions on the originating realm, they only currently get access to this information if the realm was configured to disclose the publisher/caller

above provides the basis to work around this limitation in CB.

[meejah]

We could just add _router_internal (or similar) to Message -- and thus assign anything at all that the router wants.

[oberstet]

^ yeah, agreed! that looks cleaner (only 1 attribute, and having flexibility rgd what we stick to that ..)

[meejah]

This is fixed in #1393