Returns a principal's long-term key for an enctype, derived from its password
on demand and cached; a directory-keyed principal's comes from the key source
and is never derived.
Parameters
principal: any
the principal
etype: any
the enctype
Returns Promise<any>
a promise of the key
Throws
Error for an enctype the mode withholds, or a directory-keyed
principal with no stored key of that type
Returns a principal's long-term key for an enctype, derived from its password on demand and cached; a directory-keyed principal's comes from the key source and is never derived.