Ruby Requires Chilkat v11.0.0+

Verify Signature of Alexa Custom Skill Request

See more HTTP Misc Examples

This example verifies the signature of an Alexa Custom Skill Request. Ruby

require 'chilkat'

success = false

#  This example assumes you have a web service that will receive requests from Alexa.
#  A sample request sent by Alexa will look like the following:

#  Connection: Keep-Alive
#  Content-Length: 2583
#  Content-Type: application/json; charset=utf-8
#  Accept: application/json
#  Accept-Charset: utf-8
#  Host: your.web.server.com
#  User-Agent: Apache-HttpClient/4.5.x (Java/1.8.0_172)
#  Signature: dSUmPwxc9...aKAf8mpEXg==
#  SignatureCertChainUrl: https://s3.amazonaws.com/echo.api/echo-api-cert-6-ats.pem
#  
#  {"version":"1.0","session":{"new":true,"sessionId":"amzn1.echo-api.session.433 ... }}

#  First, assume we've written code to get the 3 pieces of data we need:
signature = "dSUmPwxc9...aKAf8mpEXg=="
certChainUrl = "https://s3.amazonaws.com/echo.api/echo-api-cert-6-ats.pem"
jsonBody = "{\"version\":\"1.0\",\"session\":{\"new\":true,\"sessionId\":\"amzn1.echo-api.session.433 ... }}"

#  To validate the signature, we do the following:

#  First, download the PEM-encoded X.509 certificate chain that Alexa used to sign the message 
http = Chilkat::CkHttp.new()
sbPem = Chilkat::CkStringBuilder.new()
success = http.QuickGetSb(certChainUrl,sbPem)
if (success == false)
    print http.lastErrorText() + "\n";
    exit
end

pem = Chilkat::CkPem.new()
success = pem.LoadPem(sbPem.getAsString(),"passwordNotUsed")
if (success == false)
    print pem.lastErrorText() + "\n";
    exit
end

#  The 1st certificate should be the signing certificate.
# cert is a CkCert
cert = pem.GetCert(0)
if (pem.get_LastMethodSuccess() == false)
    print pem.lastErrorText() + "\n";
    exit
end

#  Get the public key from the cert.
pubKey = Chilkat::CkPublicKey.new()
cert.GetPublicKey(pubKey)

#  Use the public key extracted from the signing certificate to decrypt the encrypted signature to produce the asserted hash value.
rsa = Chilkat::CkRsa.new()
success = rsa.UsePublicKey(pubKey)
if (success == false)
    print cert.lastErrorText() + "\n";
    exit
end

#  RSA "decrypt" the signature.
#  (Amazon's documentation is confusing, because we're simply verifiying the signature against the SHA-1 hash
#  of the request body.  This happens in a single call to VerifyStringENC...)
rsa.put_EncodingMode("base64")
bVerified = rsa.VerifyStringENC(jsonBody,"sha1",signature)
if (bVerified == true)
    print "The signature is verified against the JSON body of the request. Yay!" + "\n";
else
    print "Sorry, not verified.  Crud!" + "\n";
end