This PR removes two berrors that aren't used anywhere in the codebase:
TooManyRequests , a holdover from AMQP, and is no longer used.
UnsupportedIdentifier, used just for rejecting IDNs, which we no longer do.
In addition, the SignatureValidation error was only used by the WFE so it is moved there and unexported.
Note for reviewers: To remove berrors.UnsupportedIdentifierError I replaced the errIDNNotSupported error in policy/pa.go with a berrors.MalformedError with the same name. This allows removing UnsupportedIdentifierError ahead of #2712 which removes the IDNASupport feature flag. This seemed OK to me, but I can restore UnsupportedIdentifierError and clean it up after 2712 if that's preferred.
Resolves#2709
This patch removes all usages of the `core.XXXError` and almost all usages of `probs` outside of the WFE and VA and replaces them with a unified internal error type. Since the VA uses `probs.ProblemDetails` quite extensively in challenges, and currently stores them in the DB I've saved this change for another change (it'll also require a migration). Since `ProblemDetails` should only ever be exposed to end-users all of its related logic should be moved into the `WFE` but since it still needs to be exposed to the VA and SA I've left it in place for now.
The new internal `errors` package offers the same convenience functions as `probs` does as well as a new simpler type testing method. A few small changes have also been made to error messages, mainly adding the library and function name to internal server errors for easier debugging (i.e. where a number of functions return the exact same errors and there is no other way to distinguish which method threw the error).
Also adds proper encoding of internal errors transferred over gRPC (the current encoding scheme is kept for `core` and `probs` errors since it'll be ideally be removed after we deploy this and follow-up changes) using `grpc/metadata` instead of the gRPC status codes.
Fixes#2507. Updates #2254 and #2505.
Daniel McCarney
Roland Bracewell Shoemaker