Authoritative currency exchange rates with citations?

I have specific requirements & would like to automate wherever possible. Currently my proficiency level is such that I’d have to do it all manually- I don’t know if what I’d like to do can even be done automatically, let alone how.

I need to convert pounds to dollars on a non-contiguous daily basis. I’d like to be able to do something like this:

ENTER_DATE-|-ENTER_POUNDS-|-AUTO_EXCHANGE_RATE-|-AUTO_DOLLARS-|-AUTO_IMF.ORG_CITATION

Any help to achieve this is appreciated.