unfortunately the documentation is lacking

I have the following example using go

// makeHmac:
//    non-exportable helper to do SHA256 HMAC
func makeHmac(data string, key string) string {
    byteKey, _ := hex.DecodeString(key)
    byteData := []byte(data)
    sig := hmac.New(sha256.New, byteKey)
    sig.Write([]byte(byteData))
    return base64.StdEncoding.EncodeToString(sig.Sum(nil))
}
[download]

still none the wiser though!

I do know that the app key provided should be treated as 32 2 byte values and not 64 1 byte values

Its this handling of the 32 2 byte values I am unsure of

thanks again for responding, its driving me slightly mad

In case this helps, I ran the Go code

package main

import  ( 
  "fmt"
  "encoding/hex"
  "encoding/base64"
  "crypto/hmac"
  "crypto/sha256"
)

func main() {
  x := makeHmac("abcdef","1234567890")
  fmt.Printf("%s\n", x)
}

func makeHmac(data string, key string) string {
  byteKey, _ := hex.DecodeString(key)  
  byteData := []byte(data)
  sig := hmac.New(sha256.New, byteKey)
  sig.Write([]byte(byteData))
  return base64.StdEncoding.EncodeToString(sig.Sum(nil))
}
[download]

and the result was

1CBMzMydzanzzzHwnZKJEswN1jqvKZiI3fwBw81t1f4=


Running this perl

#!perl
use strict;
use Digest::SHA qw( hmac_sha256_base64 );
my $digest = hmac_sha256_base64("abcdef", pack "H*",'1234567890');
print $digest;
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gave the same but without the padding

1CBMzMydzanzzzHwnZKJEswN1jqvKZiI3fwBw81t1f4
poj



1. updated with perl code

2. updated with full example code below both giving same result
GET\n08 Apr 2015 21:37:33 GMT\nd6468df6c1e8419fb5ec50f62be9a28b\n/xxxxxxxxxxxx/xxxxxxx/api/v1/users/xxxxx/factors
ApplicationID:2LIG2VOfl6swsD6rwRxBHW64dF6WK0vOO+b+VO/UbTk=
Basic :QXBwbGljYXRpb25JRDoyTElHMlZPZmw2c3dzRDZyd1J4QkhXNjRkRjZXSzB2T08rYitWTy9VYlRrPQ==

#!perl
use strict;
use Digest::SHA qw( hmac_sha256_base64 );
use MIME::Base64;

my $datestring = '08 Apr 2015 21:37:33 GMT';
my $method = 'GET';
my $appid  = 'd6468df6c1e8419fb5ec50f62be9a28b';
my $appkey = '15c7a6e1a5bd73500db29dffd0e19b6c6228b044c64348a6f5d6d470
+c54fc208';
my $path   = '/xxxxxxxxxxxx/xxxxxxx/api/v1/users/xxxxx/factors';

# build the hash string
my $step1 = "$method\\n$datestring\\n$appid\\n$path";
print "$step1\n";

# hmac, base64 and add padding
my $step3 = hmac_sha256_base64($step1, pack "H*",$appkey);
while (length($step3) % 4) {
  $step3 .= '=';
}

my $step4 = 'ApplicationID:'.$step3;
print "$step4\n";

my $step6 = "Basic :".encode_base64($step4,'');
print "$step6\n";
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// GO code
package main

import  ( 
  "fmt"
  "encoding/hex"
  "encoding/base64"
  "crypto/hmac"
  "crypto/sha256"
)

func main() {
  datestring := "08 Apr 2015 21:37:33 GMT"
  appid := "d6468df6c1e8419fb5ec50f62be9a28b"
  appkey:= "15c7a6e1a5bd73500db29dffd0e19b6c6228b044c64348a6f5d6d470c5
+4fc208"
  path  := "/xxxxxxxxxxxx/xxxxxxx/api/v1/users/xxxxx/factors"
  
  step1 := "GET\\n"+datestring+"\\n"+appid+"\\n"+path
  fmt.Printf("%s\n",step1)
  
  step4 := "ApplicationID:" + makeHmac( step1, appkey )
  fmt.Printf("%s\n",step4)
  
  step6 := "Basic :" + base64.StdEncoding.EncodeToString([]byte(step4)
+)
  fmt.Printf("%s\n", step6)
}

func makeHmac(data string, key string) string {
  byteKey, _ := hex.DecodeString(key)   
  byteData := []byte(data)
  sig := hmac.New(sha256.New, byteKey)
  sig.Write([]byte(byteData))
  return base64.StdEncoding.EncodeToString(sig.Sum(nil))
}
[download]