public static String generateIdentifier() {
        return generateIdentifier(256);
    }
Generates a unique and unpredictable identifier. Each identifier is at
least 256-bit and produced using a cryptographically-secure random
number generator. The identifier may contain characters that differ only
in case.

@return
    A unique and unpredictable identifier with at least 256 bits of
    entropy.
guacamole-ext/src/main/java/org/apache/guacamole/net/auth/IdentifierGenerator.java