[REF] Property setting on express request

[seaerchin]

Problem

Express request objects are not meant to have properties set on them (req.property = some_value), and the types reflect this (no way to adequately reflect that req has a property set).

Solution

We could adopt either

1. declaration merging (like so)
2. set properties on res.locals for all intents identical apart from naming w/ built in support from express.

The suggested solution is to use res.locals as different properties set using declaration merging will all be merged into 1 giant request type, which would be extremely confusing.