Give More Specific OAuth2.0 Error Message if Token Cannot be Refreshed

[StevenMMortimer]

Currently, when tokens cannot be refreshed a generic warning message is printed "Unable to refresh token"

httr/R/oauth-refresh.R

Line 31 in 1fc6598

warning("Unable to refresh token", call. = FALSE)

A number of more specific error messages are being trapped by known_oauth2.0_error() here

httr/R/oauth-error.r

Line 6 in 1fc6598

oauth2.0_errors <- c(

Is it possible to print out any of the trapped error messages so that we can get some more detail on how to debug if a token cannot be refreshed.