@Override
    public void setTunnel(GuacamoleTunnel tunnel) {
        this.tunnel = tunnel;
    }
Shares this active connection with the user that retrieved it, returning
a SharedConnectionDefinition that can be used to establish a tunnel to
the shared connection. If provided, access within the shared connection
will be restricted by the sharing profile with the given identifier.

@param identifier
    The identifier of the sharing profile that defines the restrictions
    applying to the shared connection, or null if no such restrictions
    apply.

@return
    A new SharedConnectionDefinition which can be used to establish a
    tunnel to the shared connection.

@throws GuacamoleException
    If permission to share this active connection is denied.
extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/activeconnection/TrackedActiveConnection.java