According to PocketMine EventPriority class doc comment, plugins SHOULD NOT change events at MONITOR level. As a plugin, SimpleAuth should follow the definition for PocketMine event priorities.
This phrase, or the phrase "NOT RECOMMENDED" mean that
there may exist valid reasons in particular circumstances when the
particular behavior is acceptable or even useful, but the full
implications should be understood and the case carefully weighed
before implementing any behavior described with this label.
As there may be possibilities that other plugins would want to, maybe log commands at the MONITOR level assuming they are not going to be cancelled (which is the actual meaning of MONITOR), it is not suitable to cancel an event at that leve.
According to PocketMine EventPriority class doc comment, plugins SHOULD NOT change events at MONITOR level. As a plugin, SimpleAuth should follow the definition for PocketMine event priorities.
According to RFC 2119:
As there may be possibilities that other plugins would want to, maybe log commands at the MONITOR level assuming they are not going to be cancelled (which is the actual meaning of MONITOR), it is not suitable to cancel an event at that leve.