Implement Authentication for Exchangerate.host

[macanudo527]

What? Why?

Exchangerate.host, the site that provides fiat prices has recently implemented access keys in order to access their pricing services. Users will be required to provide access keys in order to convert fiat amounts. The free tier allows 1000 requests/month, which should be enough for most users.

Came up in #207
Will probably fix #209

Steps to Reproduce

Try to pull any kind of report in dali_rp2 that requires a fiat conversion e.g. USD->EUR

Expected Behavior

Conversion of Fiat should be handled by exchangerate.host

Actual Behavior

Dali-RP2 exits with an error stating that the conversion can not be found on any plugin.

Priority/Severity

high - Reporting of most trades in a currency other than USD is affected.

References

Exchangerate.host
Exchangerate.host Plans
Exchangerate.host API documentation

[eprbell]

Thanks for root-causing and jumping on this, @macanudo527!

[macanudo527]

@eprbell Now that this requires an access key, I'm wondering if we should add vcrpy to record the HTTP requests and play them back. I know you are trying to keep this minimal, but vcrpy would only be necessary for testing.

[macanudo527]

The free plan only covers USD as the source (ie. we can only convert from USD to another currency). This should be okay since more often than not if the base asset is not in the user's native fiat, it is usually available in USD anyway, so the conversion is almost always USD to something else.

However, we might want to look into alternative sources for historical fx data.

[eprbell]

I wasn't familiar with vcrpy, so I took a quick look: sounds like a good idea to me. Mocking network access is very important in tests and if this helps us do that, let's go for it.

Looking for alternatives sounds like a good idea: I'll also take a look to see what's out there.