There is an update to the risk-based access documentation, which currently states that the supportsAttribute() and match() functions are required for custom attribute matchers.
Resolving the problem
The two functions, supportsAttribute() and match() are not mandatory for implementing custom attribute matchers.
In the risk-based access information center, on the page titled Implementing custom attribute matchers, under the section, Procedure, step 1 currently states:
Instead, this statement must be replaced with:
Initialize two variables in the script, processed and matched, to indicate the status of the attribute processing and matching. For example: processed = true and matched = "MATCHED".