src/main/java/org/imsglobal/lti/BasicLTIUtil.java
public static Map<String, String> cleanupProperties(
            final Map<String, String> rawProperties) {
        return cleanupProperties(rawProperties, null);
    }
public static Map<String, String> cleanupProperties(
            final Map<String, String> rawProperties) {
        return cleanupProperties(rawProperties, null);
    }
Any properties which are not well known (i.e. in
{@link BasicLTIConstants#validPropertyNames}) will be mapped to custom
properties per the specified semantics. NOTE: no blacklisting of keys is
performed.

@param rawProperties A set of properties that will be cleaned.
@return A cleansed version of rawProperties.