CertExtractor filter

[samutamm]

Resolve #467

CertExtractor filter adds values from certificates Subject or Issuer to headers.

Here's an example config:

  - kind: "CertExtractor"
    name: "cn-extractor"
    certIndex: -1
    target: "subject"
    field: "CommonName"
    headerKey: "X-AUTH-USER"

that extracts the "CommonName" field's value from the subject of the last certificate. The value is set to "X-AUTH-USER" request header.

Here's an example that sets CommonName value for new certificate: https://github.com/haoel/mTLS/blob/main/certs.go#L141

References:

• https://pkg.go.dev/crypto/x509#Certificate
• https://pkg.go.dev/crypto/x509/pkix#Name

[codecov-commenter]

Codecov Report

Merging #474 (db593d7) into main (d14d7fe) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #474      +/-   ##
==========================================
+ Coverage   80.35%   80.47%   +0.12%     
==========================================
  Files          83       84       +1     
  Lines        9685     9758      +73     
==========================================
+ Hits         7782     7853      +71     
- Misses       1461     1463       +2     
  Partials      442      442              

Impacted Files	Coverage Δ
pkg/filter/certextractor/certextractor.go	100.00% <100.00%> (ø)
pkg/object/mqttproxy/client.go	79.63% <0.00%> (-0.91%)	⬇️

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