public String getConnectionID() {
        return connectionID;
    }
Returns the ID of the connection being joined, if any. If no connection
is being joined, this returns null, and the protocol must be set.

@return The ID of the connection being joined, or null if no connection
        is being joined.
guacamole-common/src/main/java/org/apache/guacamole/protocol/GuacamoleConfiguration.java