Module: StandardSingpass::Myinfo::JwksGenerator

Extended by:
T::Sig
Defined in:
lib/standard_singpass/myinfo/jwks_generator.rb

Overview

Generates and validates the private JWKS document that gets pasted into the host application’s ‘MYINFO_PRIVATE_JWKS` env var (or equivalent). Public-facing entrypoint is the `standard_singpass:myinfo:generate_jwks` rake task; this module holds the logic so it’s testable without going through Rake.

The validator mirrors what ‘Configuration#private_jwks_json=` requires —particularly the “must have private scalar `d`” check that traps the public/private key mix-up.

Constant Summary collapse

SIG_ALG = 
T.let("ES256", String)
ENC_ALG = 
T.let("ECDH-ES+A256KW", String)
EC_CURVE = 
T.let("P-256", String)
EC_OPENSSL_NAME = 
T.let("prime256v1", String)

Class Method Summary collapse

Class Method Details

.generate(sig_kid:, enc_kid:) ⇒ Object 



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# File 'lib/standard_singpass/myinfo/jwks_generator.rb', line 23

def self.generate(sig_kid:, enc_kid:)
  sig_jwk = build_jwk(OpenSSL::PKey::EC.generate(EC_OPENSSL_NAME), kid: sig_kid, use: "sig", alg: SIG_ALG)
  enc_jwk = build_jwk(OpenSSL::PKey::EC.generate(EC_OPENSSL_NAME), kid: enc_kid, use: "enc", alg: ENC_ALG)

  jwks = { keys: [sig_jwk, enc_jwk] }

  # Defensive — the trap this module is built to prevent. If we ever
  # emit a public-only JWK from a generation path, refuse early.
  issues = validate(jwks)
  raise "Internal: generated JWKS failed self-validation:\n#{issues.join("\n")}" if issues.any?

  jwks
end

.validate(jwks) ⇒ Object 



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# File 'lib/standard_singpass/myinfo/jwks_generator.rb', line 41

def self.validate(jwks)
  return ["root is not a JSON object (got #{jwks.class})"] unless jwks.is_a?(Hash)

  keys = jwks["keys"] || jwks[:keys]
  return ["missing 'keys' array"] unless keys.is_a?(Array)

  issues = []

  sig_keys = keys.select { |k| k.is_a?(Hash) && key_field(k, :use) == "sig" }
  enc_keys = keys.select { |k| k.is_a?(Hash) && key_field(k, :use) == "enc" }

  issues << "expected exactly one sig key (use=\"sig\"), got #{sig_keys.size}" unless sig_keys.size == 1
  issues << "expected at least one enc key (use=\"enc\"), got 0" if enc_keys.empty?

  # RFC 7517 §4.5: kid values within a JWKS should be distinct so a
  # consumer can pick keys unambiguously. The runtime config loader
  # selects by `use`, so a duplicate kid wouldn't blow up at boot —
  # but Singpass may behave differently, and a duplicate is almost
  # always an operator copy/paste mistake.
  hashlike_keys = keys.grep(Hash)
  kid_counts = hashlike_keys.group_by { |k| key_field(k, :kid) }.transform_values(&:size)
  kid_counts.each do |kid, count|
    next if count <= 1
    issues << "duplicate kid #{kid.inspect} appears #{count} times — kids must be unique within a JWKS (RFC 7517 §4.5)"
  end

  keys.each_with_index do |k, i|
    unless k.is_a?(Hash)
      issues << "keys[#{i}] is not an object (got #{k.class})"
      next
    end
    kid = key_field(k, :kid)
    use = key_field(k, :use)
    label = "keys[#{i}] kid=#{kid.inspect} use=#{use.inspect}"

    d = key_field(k, :d)
    kty = key_field(k, :kty)
    crv = key_field(k, :crv)
    alg = key_field(k, :alg)

    # Public-only-key trap. Without `d` the JWK is public-only and
    # cannot sign or decrypt — every Singpass call fails at runtime.
    # `.blank?` matches the runtime config loader's check so the
    # validator and the loader accept the same set of inputs.
    issues << "#{label}: missing 'd' (public-only — re-export with include_private: true)" if d.blank?
    issues << "#{label}: kty=#{kty.inspect} expected \"EC\"" unless kty == "EC"
    issues << "#{label}: crv=#{crv.inspect} expected \"P-256\" (FAPI 2.0 requires EC P-256)" unless crv == EC_CURVE

    case use
    when "sig"
      issues << "#{label}: alg=#{alg.inspect} expected \"#{SIG_ALG}\"" unless alg == SIG_ALG
    when "enc"
      issues << "#{label}: alg=#{alg.inspect} expected \"#{ENC_ALG}\"" unless alg == ENC_ALG
    else
      issues << "#{label}: use=#{use.inspect} expected \"sig\" or \"enc\""
    end
  end

  issues
end