x-pack/filebeat/input/httpjson: Add hexDecode function

[darshan-elastic]

• Enhancement

What does this PR do?

This adds template helper function for decoding hexadecimal string, output will be in bytes representation.

Why is it important?

This feature is needed for authentication with some APIs. For example, https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html for the AWS Security Hub integration package.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

[elasticmachine]

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• Start Time: 2022-06-20T06:00:00.158+0000

• Duration: 80 min 26 sec

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[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[andrewkroh]

This feature is needed for authentication with some APIs. For example, https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html for the AWS Security Hub integration package.

Can you provide an example template showing how this will be used in that context.

[darshan-elastic]

This feature is needed for authentication with some APIs. For example, https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html for the AWS Security Hub integration package.

Can you provide an example template showing how this will be used in that context.

Sure, we are trying to use it in that context as follows:

Reference: https://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-python

def sign(key, msg):
    return hmac.new(key, msg.encode("utf-8"), hashlib.sha256).digest()

def getSignatureKey(key, dateStamp, regionName, serviceName):
    kDate = sign(("AWS4" + key).encode("utf-8"), dateStamp)
    kRegion = sign(kDate, regionName)
    kService = sign(kRegion, serviceName)
    kSigning = sign(kService, "aws4_request")
    return kSigning

Example template:

[[(hexDecode (hmac "sha256" (hexDecode (hmac "sha256" (hexDecode (hmac "sha256" (hexDecode (hmac "sha256" "AWS4wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY" "20120215")) "us-east-1")) "iam")) "aws4_request"))]]

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b httpjson_hex_decode upstream/httpjson_hex_decode
git merge upstream/main
git push upstream httpjson_hex_decode

[efd6]

Thanks