AWS API in R - Added Authorization Header but getting InvalidSignatureException - r

Question

I am trying to use AWS API in R. I am using R so that i can add it to an exisiting ShinyApp (which is a web application build in R).
This API: https://docs.aws.amazon.com/connect/latest/APIReference/API_GetCurrentMetricData.html
Using signature version 4:
https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html
I have added the 'Authorization' details to the header as per AMZ documentation, and the exact header works perfectly in python, but strangely not in R and returns an error saying 'InvalidSignatureException'.
My guess is that i have got something wrong with the variables in the POST function. I've quite a few different arrangements of the POST variables to try and get it to work but nothing seems to help.
This is the python code which works:
import requests
url = "https://connect.eu-central-1.amazonaws.com/metrics/current/XXXXXXX"
payload = "{\r\n \"InstanceId\" : \"XXXXXXX\",\r\n \"Filters\" : {\r\n \"Queues\" : [\r\n \"XXXXXXX\",\r\n \"arn:aws:connect:eu-central-1:XXXXXXX:instance/XXXXXXX/queue/XXXXXXX\"\r\n ]\r\n },\r\n \"CurrentMetrics\" : [\r\n {\r\n \"Name\" : \"AGENTS_ONLINE\",\r\n \"Unit\" : \"COUNT\"\r\n },\r\n {\r\n \"Name\" : \"AGENTS_AVAILABLE\",\r\n \"Unit\" : \"COUNT\"\r\n },\r\n {\r\n \"Name\" : \"OLDEST_CONTACT_AGE\",\r\n \"Unit\" : \"SECONDS\"\r\n },\r\n {\r\n \"Name\": \"AGENTS_ERROR\",\r\n \"Unit\": \"COUNT\"\r\n }\r\n ]\r\n}\r\n "
headers = {
'Content-Type': "application/json",
'X-Amz-Content-Sha256': "XXXXXXX",
'Host': "connect.eu-central-1.amazonaws.com",
'X-Amz-Date': "20190724T162517Z",
'Authorization': "AWS4-HMAC-SHA256 Credential=XXXXXXX/20190724/eu-central-1/connect/aws4_request, SignedHeaders=content-type;host;x-amz-content-sha256;x-amz-date, Signature=XXXXXXX",
}
response = requests.request("POST", url, data=payload, headers=headers)
print(response.text)
My attempt to write in R. (returns x-amzn-ErrorType: InvalidSignatureException)
library(httr)
library(jsonlite)
request_body_json <-
'{
"InstanceId" : "xxxxxxxxxx",
"Filters" : {
"Queues" : [
"xxxxxxxxxx",
"arn:aws:connect:eu-central-1:xxxxxxxxxx:instance/xxxxxxxxxx/queue/xxxxxxxxxx"
]
},
"CurrentMetrics" : [
{
"Name" : "AGENTS_ONLINE",
"Unit" : "COUNT"
},
{
"Name" : "AGENTS_AVAILABLE",
"Unit" : "COUNT"
},
{
"Name" : "OLDEST_CONTACT_AGE",
"Unit" : "SECONDS"
},
{
"Name": "AGENTS_ERROR",
"Unit": "COUNT"
}
]
}'
hdrs <- list(
'Content-Type'= "application/json",
'X-Amz-Content-Sha256'= "XXXXXXX",
'Host'= "connect.eu-central-1.amazonaws.com",
'X-Amz-Date'= "20190724T162517Z",
'Authorization'= "AWS4-HMAC-SHA256 Credential=XXXXXXX/20190724/eu-central-1/connect/aws4_request, SignedHeaders=content-type;host;x-amz-content-sha256;x-amz-date, Signature=XXXXXXX"
)
a <- POST(
url = "https://connect.eu-central-1.amazonaws.com/metrics/current/xxxxxxxxxx"
,do.call(add_headers,hdrs)
,verbose(info = TRUE)
,body = request_body_json
,encode = "json"
)

Answer 1

Fixed and added the authorisations steps in too.
# Librarys used
library(httr)
library(jsonlite)
library(aws.signature)
#gather variables
host <- "connect.eu-central-1.amazonaws.com"
sha <- "xxxx"
amzdate <- format(Sys.time(), "%Y%m%dT%H%M%SZ",tz = "UTC")
payload <-
'{
"InstanceId" : "xxxx-xxxx-xxxx-xxxx-xxxx",
"Filters" : {
"Queues" : [
"xxxx-xxxx-xxxx-xxxx"
]
},
"CurrentMetrics" : [
{
"Name" : "OLDEST_CONTACT_AGE",
"Unit" : "SECONDS"
},
{
"Name": "CONTACTS_IN_QUEUE",
"Unit": "COUNT"
}
]
}'
content_type <-"application/json"
url_api <-"https://connect.eu-central-1.amazonaws.com/metrics/current/xxxx-xxxx-xxxx-xxxx"
region <- "eu-central-1"
service <- "connect"
verb <- "POST"
action <- "/metrics/current/xxxx-xxxx-xxxx-xxx-xxxx"
key <- "xxxx"
secret <- "xxxx"
#headers so far (can't add signature yet)
hdrs <- list('Content-Type' = content_type,
Host = host,
'x-amz-content-sha256' = sha,
'x-amz-date' = amzdate)
#get v4 signature
sig <- signature_v4_auth(datetime = amzdate,
region = region,
service = service,
verb = verb,
action = action,
query_args = list(),
canonical_headers = hdrs,
request_body = payload,
key = key,
secret = secret,
session_token = NULL,
query = FALSE,
algorithm = "AWS4-HMAC-SHA256")
#add signature header to header
auth <- sig$SignatureHeader
a <- httr::VERB(verb = "POST"
,url = url_api
,encode = 'json'
,content_type_json()
,body = payload
,httr::add_headers(
'Content-Type' = content_type,
Authorization = auth,
Host = host,
`X-Amz-Content-Sha256` = sha,
`X-Amz-Date` = amzdate)
)
results <- content(a,"parsed")