API access, Hashing query, possibly related to character encoding - r

Question

Its going to be impossible to provide a reproducible example for this as it has to do with accessing a particular API - apologies in advance. I am trying to access the edinburgh fringe festivals API through R. The documentation says the following:
Authentication
An access key is required for all requests to the API and can be
obtained by registration. This key, combined with the signature
explained below, is required to get any access to the API. If you do
not provide an access key, or provide an invalid key or signature, the
server will return an HTTP 403 error.
Your secret token is used to calculate the correct signature for each
API request and must never be disclosed. Once issued, it is never
transmitted back or forward. The API server holds a copy of your
secret token, which it uses to check that you have signed each request
correctly.
You calculate the signature using the HMAC-SHA1 algorithm:
Build the full API request URL, including your access key but excluding the server domain - eg /events?festival=book&key=12345. See
the note below on URL encoding.
Calculate the hmac hash of the url using the sha1 algorithm and your secret token as the key.
Append the hex-encoded hash to your url as the signature parameter
URL encoding in queries
You should calculate the signature after URL-encoding any parameters -
for example, to search for the title "Mrs Brown" you would first build
the URL /events?title=Mrs%20Brown&key=12345 and then sign this string
and append the signature.
Signature encoding
Some languages - notably C# - default to encoding hashes in UTF-16.
Ensure your signature is encoded in plain ASCII hex or it will not be
valid.
What I have tried so far is below:
library(digest)
library(jsonlite)
source("authentication.R") # credentials stored here
create the query string
query <- paste0('/events?festival=demofringe&size=20&from=1&key=', API_KEY)
create the hashed query
sig <- hmac(SECRET_SIGNING_KEY, query, algo="sha1")
create the final url
url <- paste0('https://api.edinburghfestivalcity.com', query, '&signature=', sig)
submit to the API
results <- fromJSON(url)
and I get the error:
Error in open.connection(con, "rb") : HTTP error 417.
I'm not sure that the signature is ASCII encoded as per the documentation. Does anyone know how to debug this situation? I have tried iconv() to try and convert the encoding and when I call Encoding() on the character object it returns "unknown". I have also tried saving both files in RStudio with "save with encoding" set to ASCII and I have tried sourcing the authentications with encoding = "ASCII".
Incidentally when I paste the final url into a browser, I get the following error:
Invalid Accept header value. ['application/json', 'application/json;ver=2.0'] are supported

Answer 1

That's a server error. It should understand that
Accept: application/json, text/*, */*
Matches application/json. Note that instead of modifying jsonlite, it is beter to manually retrieve the response form the server, and then feed it to jsonlite.
library(httr)
library(jsonlite)
req <- GET(your_url, accept("application/json")
json <- content(req, as = 'text')
data <- fromJSON(json)

Answer 2

In the end, I solved this problem by editing the jsonlite::fromJSON() function. namely the line
curl::handle_setheaders(h, Accept = "application/json, text/*, */*")
I changed to
curl::handle_setheaders(h, Accept = "application/json")
I then also had to point to the internal functions with jsonlite:::. Now it works fine.