Here is as far as I got. I receive a "400 Not Authorized", maybe this is due to the fact that my openpaths account is not connected to foursquare, maybe something is wrong with the code. Please try it out!
Required packages:
library(RCurl)
library(digest)
library(base64)
Some functions borrowed/adapted from ROAuth:
## Get a random sequence of characters.
## Nonce - number used only once.
genNonce <- function(len = 15L + sample(1:16, 1L)) {
els <- c(letters, LETTERS, 0:9, "_")
paste(sample(els, len, replace = TRUE), collapse = "")
}
## this function is derived from utils::URLencode
## Characters not in the unreserved character set ([RFC3986] section 2.3) MUST be encoded
## unreserved = ALPHA, DIGIT, '-', '.', '_', '~'
## cf. http://oauth.net/core/1.0/#encoding_parameters
encodeURI <- function(URI, ...) {
if (!is.character(URI)) {
URI
} else {
OK <- "[^-A-Za-z0-9_.~]"
x <- strsplit(URI, "")[[1L]]
z <- grep(OK, x)
if (length(z)) {
y <- sapply(x[z], function(x) paste("%", toupper(as.character(charToRaw(x))),
sep = "", collapse = ""))
x[z] <- y
}
paste(x, collapse = "")
}
}
## we escape the values of the parameters in a special way that escapes
## the resulting % prefix in the escaped characters, e.g. %20 becomes
## %2520 as %25 is the escape for %
## cf. http://tools.ietf.org/html/rfc5849#section-3.4.1.3.2
normalizeParams <- function(params, escapeFun) {
names(params) <- sapply(names(params), escapeFun, post.amp = TRUE)
params <- sapply(params, escapeFun, post.amp = TRUE)
## If two or more parameters share the same name, they are sorted by their value.
params <- params[order(names(params), params)]
return(paste(names(params), params, sep = "=", collapse = "&"))
}
## From Ozaki Toru's code at https://gist.github.com/586468
signWithHMAC <- function(key, data) {
blockSize <- 64
hashlength <- 20
innerpad <- rawToBits(as.raw(rep(0x36, blockSize)))
outerpad <- rawToBits(as.raw(rep(0x5C, blockSize)))
zero <- rep(0 ,64)
HexdigestToDigest <- function(digest) {
as.raw(strtoi(substring(digest, (1:hashlength)*2-1,
(1:hashlength)*2), base=16))
}
mac <- function(pad, text) {
HexdigestToDigest(digest(append(packBits(xor(key, pad)), text),
algo='sha1', serialize=FALSE))
}
if(nchar(key) >= 64) {
keyDigested <- digest(key, algo="sha1", serialize=FALSE)
key <- intToUtf8(strtoi(HexdigestToDigest(keyDigested), base=16))
}
key <- rawToBits(as.raw(append(utf8ToInt(key), zero)[1:blockSize]))
base64(mac(outerpad, mac(innerpad, charToRaw(data))))[1]
}
## Sign an request made up of the URL, the parameters as a named character
## vector the consumer key and secret and the token and token secret.
signRequest <- function(uri, consumerKey, consumerSecret, params=character(),
oauthKey = "", oauthSecret = "", httpMethod = "GET",
nonce = genNonce(),
timestamp = Sys.time()) {
httpMethod <- toupper(httpMethod)
params["oauth_nonce"] <- nonce
params["oauth_timestamp"] <- as.integer(timestamp)
params["oauth_consumer_key"] <- consumerKey
params["oauth_signature_method"] <- 'HMAC-SHA1'
params["oauth_version"] <- '1.0'
if(oauthKey != "") params["oauth_token"] <- oauthKey
odat <- paste(
encodeURI(httpMethod), encodeURI(uri),
encodeURI(normalizeParams(params, encodeURI), post.amp = TRUE),
sep = "&"
)
okey <- encodeURI(consumerSecret)
if(oauthSecret != "") okey <- paste(okey, encodeURI(oauthSecret), sep = "&")
params["oauth_signature"] <- signWithHMAC(okey, odat)
return(params)
}
Now this function tries to replicate the example at the openpaths website:
openpaths <- function(
access_key=getOption("openpaths.access_key"),
secret_key=getOption("openpaths.secret_key"),
curl=getCurlHandle()) {
uri <- 'https://openpaths.cc/api/1'
params <- signRequest(uri, consumerKey=access_key, consumerSecret=secret_key)
oa_header <- paste(names(params), params, sep="=", collapse=",")
ret <- getURL(
uri,
curl=curl,
.opts=list(
header=TRUE,
verbose=TRUE,
httpheader=c(Authorization=paste("OAuth ", oa_header, sep="")),
ssl.verifypeer = TRUE,
ssl.verifyhost = TRUE,
cainfo = system.file("CurlSSL", "cacert.pem", package = "RCurl")
)
)
return(ret)
}
