Upload File to Amazon S3

How can I perform this upload with wwipstuff?

Currently I'm getting result=403 Forbidden

LOCAL loIP as wwipstuff OF wwipstuff
loIP=NEWOBJECT('wwipstuff','wwipstuff')

LOCAL lcPolicyDoc,lcPolicyDocEncoded,lcSignature
TEXT TO lcPolicyDoc NOSHOW PRETEXT 15
{"expiration": "2015-01-01T00:00:00Z",
  "conditions": [ 
    {"bucket": "mybucket"}, 
    ["starts-with", "$key", ""],
    {"acl": "public-read"},
    ["starts-with", "$Content-Type", ""],
    ["content-length-range", 0, 1048576]
  ]
}
ENDTEXT
lcPolicyDocEncoded=STRCONV(lcPolicyDoc,13)
lcSignature=hmac(lcPolicyDocEncoded,"SecretAccessKey",1)

? lcSignature

loIP.cHTTPProxyName=""
IF loIP.HTTPConnect("mybucket.s3.amazonaws.com",,,.T.)=0
	loIP.encodefile
	lcBuffer=loIP.encodefile("c:\images\myimage.jpg")
	
	loIP.AddPostKey('AWSAccessKeyId',"MyAccessKeyID")
	loIP.AddPostKey('bucket',"mybucket")
	loIP.AddPostKey('policy',lcPolicyDocEncoded)
	loIP.AddPostKey('signature',lcSignature)
	loIP.AddPostKey("success_action_redirect","http:"+"//localhost/")
	
	** image specific 
	loIP.AddPostKey('acl',"public-read")
	loIP.AddPostKey('Content-Type',"image/jpeg")
	
	loIP.AddPostKey('key',"myimage.jpg")
	loIP.AddPostKey('file',lcBuffer)
	
	lcOutput=""
	lnSize=0
	
	lnResult=loIP.HTTPGetEx([],@lcOutput,@lnSize)
	loIP.HTTPClose
	IF lnResult=0
		** good
		? 'success'
	ELSE
		? 'error '+loIP.cerrormsg+' '+lcOutput
	ENDIF
ELSE
	? 'error '+loIP.cerrormsg+' '+lcOutput
ENDIF