private Set<String> getToleratedAuthenticationProviders() {

        // Parse list of auth providers whose internal failures should be
        // tolerated
        try {
            return environment.getProperty(SKIP_IF_UNAVAILABLE, Collections.<String>emptySet());
        }

        // Use empty set by default if property cannot be parsed
        catch (GuacamoleException e) {
            logger.warn("The list of authentication providers specified via the \"{}\" property could not be parsed: {}", SKIP_IF_UNAVAILABLE.getName(), e.getMessage());
            logger.debug("Unable to parse \"{}\" property.", SKIP_IF_UNAVAILABLE.getName(), e);
            return Collections.<String>emptySet();
        }

    }
Returns the set of identifiers of all authentication providers whose
internal failures should be tolerated during the authentication process.
If the identifier of an authentication provider is within this set,
errors during authentication will result in the authentication provider
being ignored for that authentication attempt, with the authentication
process proceeding as if that authentication provider were not present.
By default, errors during authentication halt the authentication process
entirely.

@return
    The set of identifiers of all authentication providers whose
    internal failures should be tolerated during the authentication
    process.
guacamole/src/main/java/org/apache/guacamole/extension/ExtensionModule.java