This commit updates CTPolicy & the RA to return a distinct error when
the RA is unable to fetch the required SCTs for a certificate when
processing an issuance. This error type is plumbed up to the WFE/WFE2
where the `web/probs.go` code converts it into a server internal error
with a suitable user facing error.
For a long time now the WFE has generated URLs based on the incoming
request rather than a hardcoded BaseURL. BaseURL is no longer set in the
prod configs.
This also allows factoring out relativeEndpoint into the web package.
* Move probs.go to web.
* Move probs_test.go
* Factor out probs.go from wfe
* Move context.go
* Extract context.go into web package.
* Add a constructor for TopHandler.
This is shared code between both packages. Better to have it in a single shared place.
In the process, remove the unexported signatureValidationError, which was unnecessary; all returned errors from checkAlgorithm get turned into Malformed.
Jacob Hoffman-Andrews