415 code using httr and RCurl, but not just curl

Question

I'm trying to write a function that handles some of the authentication for Spotify's API. I can get it to work with a fairly simple curl command, but when I try to use httr or RCurl, I get 415 Unsupported Media Type responses. I'm somewhat at a loss at this point. I've gotten POST(), and GET() to work with this API already, but this endpoint is not working.

Using httr:

response <- POST('https://accounts.spotify.com/api/token',
                 accept_json(),
                 add_headers('Authorization'=paste('Basic',base64(paste(client_id,':',client_secret)),sep=' ')),
                 body=list(grant_type='client_credentials'),
                 encode='json')

I get a 415 status_code(response)

Using RCurl:

httpheader <- c('Authorization'=paste('Basic ',base64(paste(client_id,':',client_secret,sep='')),sep=''))
jsonbody <- toJSON(list(grant_type='client_credentials'))
postForm('https://accounts.spotify.com/api/token/',
         postfields=jsonbody,
         # grant_type='client_credentials',
         .opts = list(httpheader=httpheader,
                      verbose=TRUE))

postForm output:

* Hostname was NOT found in DNS cache
*   Trying 194.132.198.228...
* Connected to accounts.spotify.com (194.132.198.228) port 443 (#9)
* found 173 certificates in /etc/ssl/certs/ca-certificates.crt
*    server certificate verification OK
*    common name: *.spotify.com (matched)
*    server certificate expiration date OK
*    server certificate activation date OK
*    certificate public key: RSA
*    certificate version: #3
*    subject: C=SE,ST=Stockholm,L=Stockholm,O=Spotify AB,CN=*.spotify.com
*    start date: Tue, 15 Apr 2014 00:00:00 GMT

*    expire date: Wed, 21 Jun 2017 12:00:00 GMT

*    issuer: C=US,O=DigiCert Inc,CN=DigiCert SHA2 Secure Server CA
*    compression: NULL
*    cipher: AES-256-CBC
*    MAC: SHA256
> POST /api/token/ HTTP/1.1
Host: accounts.spotify.com
Accept: */*
Authorization: Basic ZWE...zE=
Content-Length: 182
Expect: 100-continue
Content-Type: multipart/form-data; boundary=------------------------95ce917e6abd21b1

< HTTP/1.1 100 Continue
< HTTP/1.1 415 Unsupported Media Type
* Server nginx is not blacklisted
< Server: nginx
< Date: Wed, 21 Oct 2015 01:38:39 GMT
< Content-Length: 990
< Connection: keep-alive
< Keep-Alive: timeout=10
* HTTP error before end of send, stop sending
< 
* Closing connection 9
Error: Unsupported Media Type

using curl through a system call (or from command line) actually works:

system(
  paste('curl https://accounts.spotify.com/api/token -H "Authorization: Basic ',
        base64(paste(client_id,':',client_secret,sep='')),
        '" -d grant_type=client_credentials ',
        sep=''),
  intern=TRUE)

Not sure if this is useful at this point.

> devtools::session_info()
Session info -------------------------------------------------------------------------------------------------------
 setting  value                       
 version  R version 3.2.2 (2015-08-14)
 system   x86_64, linux-gnu           
 ui       RStudio (0.99.441)          
 language en_US                       
 collate  en_US.UTF-8                 
 tz       <NA>                        
 date     2015-10-20                  

Packages -----------------------------------------------------------------------------------------------------------
 package    * version    date       source                          
 bitops       1.0-6      2013-08-17 CRAN (R 3.2.1)                  
 caTools      1.17.1     2014-09-10 CRAN (R 3.2.1)                  
 colorspace   1.2-6      2015-03-11 CRAN (R 3.2.1)                  
 curl         0.9.3      2015-08-25 CRAN (R 3.2.2)                  
 DBI          0.3.1      2014-09-24 CRAN (R 3.2.1)                  
 devtools   * 1.9.1.9000 2015-10-21 Github (hadley/devtools@0295d20)
 digest       0.6.8      2014-12-31 CRAN (R 3.2.1)                  
 git2r        0.11.0     2015-08-12 CRAN (R 3.2.2)                  
 httr       * 1.0.0.9000 2015-10-21 Github (hadley/httr@f7593b7)    
 jsonlite   * 0.9.17     2015-09-06 CRAN (R 3.2.2)                  
 knitr        1.11       2015-08-14 CRAN (R 3.2.2)                  
 magrittr     1.5        2014-11-22 CRAN (R 3.2.1)                  
 memoise      0.2.1      2014-04-22 CRAN (R 3.2.1)                  
 R6           2.1.1      2015-08-19 CRAN (R 3.2.2)                  
 Rcpp         0.12.1     2015-09-10 CRAN (R 3.2.2)                  
 RCurl      * 1.96-0     2015-07-27 local                           
 RJSONIO    * 1.3-0      2014-07-28 CRAN (R 3.2.2)                  
 roxygen2     4.1.1      2015-04-15 CRAN (R 3.2.1)                  
 RSelenium  * 1.3.5      2014-10-26 CRAN (R 3.2.2)                  
 rstudioapi   0.3.1      2015-04-07 CRAN (R 3.2.1)                  
 stringi      0.5-5      2015-06-29 CRAN (R 3.2.2)                  
 stringr    * 1.0.0      2015-04-30 CRAN (R 3.2.2)                  
 XML        * 3.98-1.3   2015-06-30 CRAN (R 3.2.2)        

Answer 1

That particular Spotify endpoint is looking for Content-Type: application/x-www-form-urlencoded vs JSON as you have it. This should work (it did for me):

library(httr)

response <- POST('https://accounts.spotify.com/api/token',
                 accept_json(),
                 authenticate(Sys.getenv("SPOTIFY_CLIENT_ID"), Sys.getenv("SPOTIFY_CLIENT_SECRET")),
                 body=list(grant_type='client_credentials'),
                 encode='form',
                 verbose())

(You can remove the verbose() in production)

Note the encode='form' but also note that you can use authenticate() vs build your own basic auth header (I store all keys in env variables, hence the use of Sys.getenv().

Answer 2

A 415 response code usually indicates you are specifying a Content-Type that the server doesn't support, or maybe you aren't specifying one at all.

415 Unsupported Media Type: The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.

The postForm example you have above is specifying "Content-Type: multipart/form-data;". I can reproduce the 415 response with the following curl:

curl -v -X POST 'https://accounts.spotify.com/api/token' -H 'Content-Type: multipart/form-data'

If you change the content type to application/x-www-form-urlencoded it should work.

curl -v -X POST 'https://accounts.spotify.com/api/token' -H 'Content-Type: application/x-www-form-urlencoded'