@Override
    public URI parseValue(String value) throws GuacamoleException {

        if (value == null)
            return null;

        // Verify wildcard prefix is present
        Matcher matcher = WILDCARD_URI_PATTERN.matcher(value);
        if (matcher.matches()) {

            // Strip wildcard prefix from URI and verify a valid hostname is
            // still present
            URI uri = super.parseValue(matcher.group(1) + matcher.group(2));
            if (uri.getHost() != null)
                return uri;

        }

        // All other values are not valid wildcard URIs
        throw new GuacamoleServerException("Value \"" + value
            + "\" is not a valid wildcard URI.");

    }
Regular expression that broadly matches URIs that contain wildcards in
their hostname. This regular expression is NOT strict and will match
invalid URIs. It is only strict enough to recognize a wildcard hostname
prefix.
extensions/guacamole-auth-sso/modules/guacamole-auth-sso-ssl/src/main/java/org/apache/guacamole/auth/ssl/conf/WildcardURIGuacamoleProperty.java