ORTB error responses

[bretg]

There's been a request to redesign how PBS responds to errors.

Currently when PBS responds with an HTTP error code (e.g. 400), the body of the response is just a string.

This issue tracks discussion for returning ORTB JSON responses with a No-Bid-Response code when PBS returns an error. e.g.

{nbr: x, seatbid [], ext.prebid.errors:{...} }

This could be a breaking change, so would have to happen in a major release, and/or be combined with a client request flag defining how they want the server to respond to errors. e.g. ext.prebid.ortberrors:true.

Another topic for discussion is whether to combine this with a more general review and refactoring of error codes in general.

[SyntaxNode]

We should discuss how Prebid Server responds in the case of a request with invalid json.

PBS-Go will return an error which includes details of the invalid json. There's a request from @maditya to return an error message without details because the current behavior violates best practices of not directly returning a framework error message. They also expressed potential security issues with exposing an internal error message.

[pm-nikhil-vaidya]

PRD

https://docs.google.com/document/d/1JiLWHHpsq9ou-pV7nPk9UVHl6hkj2ke2tTct2tcxiOU