public URI getRedirectUri() throws GuacamoleException {
        return environment.getRequiredProperty(DUO_REDIRECT_URI);
    }
Return the callback URI that will be called by Duo after authentication
with Duo has been completed. This should be the URI to return the user
to the Guacamole interface, and will be a full URI.

@return
    The URL for Duo to use to callback to the Guacamole interface after
    authentication has been completed.

@throws GuacamoleException 
    If guacamole.properties cannot be read, or if the property is not
    defined.
extensions/guacamole-auth-duo/src/main/java/org/apache/guacamole/auth/duo/conf/ConfigurationService.java