[Docs] Document how to use Express middleware for authorization

[dhmlau]

Description

Document how to use Express middleware for authorization.

Related to: #1293

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[dhmlau]

@deepakrkris @emonddr @jannyHou, could you please review if that's something we can do today and/or we have documentation already covered? Thanks.

[jannyHou]

After #5118 landed it should be easier for us to add express middleware.

@deepakrkris has a PoC PR showing use Express middleware for authentication in #5302. We can find some outstanding middleware for authorization and try the similar approach.