Add request signing example in Ruby

ps-api-examples/message-signing/ruby/Gemfile

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+source "https://rubygems.org"
+
+gem "faraday", "~>2", "<3"

ps-api-examples/message-signing/ruby/Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    base64 (0.2.0)
+    faraday (2.8.1)
+      base64
+      faraday-net_http (>= 2.0, < 3.1)
+      ruby2_keywords (>= 0.0.4)
+    faraday-net_http (3.0.2)
+    ruby2_keywords (0.0.5)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  faraday (~> 2, < 3)
+
+BUNDLED WITH
+   2.1.4

ps-api-examples/message-signing/ruby/signing_example.rb

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+require "digest" # For SHA-512
+require "base64" # for encoding
+require "openssl" # for cryptography
+require "time" # ISO8601 formatting
+require "faraday" # Adapter for most HTTP clients
+
+class RequestSigningMiddleware < Faraday::Middleware
+  # @option key_id[String] UID of the signing key; found in the Starling dev portal
+  # @option key[OpenSSL::PKey::RSA] the private key used to sign requests
+  # def initialize(app, key_id:, key:)...
+  def on_request(env)
+    env[:request_headers].merge!(generate_auth_headers(env, Time.now))
+  end
+
+  def generate_auth_headers(env, at_request_time)
+    body_to_digest = (env[:request_body].nil? || env[:request_body].empty?) ? "X" : env[:request_body]
+    raise "The request_body must be a String - this middleware has to be mounted below :json" unless body_to_digest.is_a?(String)
+
+    body_digest = Base64.strict_encode64(Digest::SHA512.digest(body_to_digest))
+    date = at_request_time.utc.iso8601
+    string_to_sign = "(request-target): #{request_target(env)}\nDate: #{date}\nDigest: #{body_digest}"
+    msg_digest = Base64.strict_encode64(key.sign("SHA256", string_to_sign))
+
+    {
+      "Authorization" => "Signature keyid=\"#{key_id}\",algorithm=\"rsa-sha256\",headers=\"(request-target) Date Digest\",signature=\"#{msg_digest}\"",
+      "Digest" => body_digest,
+      "Date" => date
+    }
+  end
+
+  private
+
+  # Should be the request path + eventually query string if set
+  def request_target(env)
+    path_and_query = [env[:url].path, env[:url].query].compact.join("?")
+    "#{env[:method].downcase} #{path_and_query}"
+  end
+
+  def key_id
+    options.fetch(:key_id)
+  end
+
+  def key
+    options.fetch(:private_key)
+  end
+end
+Faraday::Request.register_middleware(starling_request_signing: RequestSigningMiddleware)
+
+
+# You can generate a new keypair using
+#   keypair = OpenSSL::PKey::RSA.new(2048)
+# For the signing you need the private key only
+#   pem = keypair.private_to_pem (if you use Ruby's openssl version 3 or above)
+# or
+#   pem = keypair.to_pem (older "openssl" versions)
+private_key = OpenSSL::PKey::RSA.new(<<~PEM)
+  -----BEGIN RSA PRIVATE KEY-----
+  MIIEpAIBAAKCAQEAyQtOhiSj+7+UblUGADTPDGTuXP1YuLSE25+R+Lj71AmQUD+6
+  qcAu4CUdfJ48p13Bg7veY0Dxk9VmSnZ12IST8dLfM80625ILMpLEdESihPzaCnjE
+  /Y4eGlFCefIL9b4DUasOaXOJzyvloS1/tQX/cwT8yAIfK/hXlsq38dt50w+9i58C
+  k9dhrq5nxAXwIfkqytcSyQipIYUkp8qyKTpsswO0m/LOk8KRd/NybIxCD+cVm4eQ
+  0xfFFa8jhN9CpP5onUDGugVm2zlqheaAYS9GxEJc/Z5oh78tuyuH+PGv+cRxNUCq
+  y0pZHsK+qp8tZGRqsBprgqAV4itZ7M6UiKPHBQIDAQABAoIBACSjbl6M++OLwPmw
+  fgT4mskX9ca1lv8mStYZiQkqcR5t1cKCMrrv3rsTmIGW9tfLgtJGoRs2gTAfYmJs
+  n0JjuvCFrQ6sNq9AONExJSNJRNL2n6fr5X6N8Vd7eqFtppdU1xcBlQFLwJAkYFdU
+  yuLLIogsHwM2O8cQHapJ7GbjyBpZ/6LkF6Cz80Nnud5mKrJIOIwzcS5/rTszlVdA
+  cdtwAfHZIKWqccMxd/ukZ3s3cFgub+DtW49uYdfTOXbPsWbZbyTugBIPvP7rldeI
+  hm+AExHmq7/q0m3baJuIFm7ISNd/noS4guRAbtgk1pvVemwOad3gq1geKTo1uStO
+  tXvJz8sCgYEA8mHBNH7iezDpA1IMgsKaZQwuWgVWKp9OVzMXyYuQ6Be57YQr2d1O
+  skMNcCV+wJGGDX79PEJvp/t6kZDrAq7duYJqKtRdRfu+99R3tsYz6eY4G4uNp0mF
+  gFdRdMtOTZHVhtk3E4zEi2I7i/I8Ce4WbPVB27kR4gTNx7tNKhRELKMCgYEA1Fb7
+  CnotoHf76kyoEkyrq+WP/TdLkpsabDZRrjiET4cbNj6f8nWLdN5yIfcrRBe5b5wU
+  bnZQsuxgofwo+To9ECa7McvVI5z3UX/mq4Lbf85CYMUUKouz8GURxcgvbCRMXlJ/
+  ozWp0mWQwJx/2t0TH6SxYAaRZk1hyRX50Qc8EDcCgYAJXjfedI0CX+iRpUkwgJ8B
+  CtB70Dr9WLzpZ+Mieg92uPwJrxMWz5PsFeVeEUTt4nIA8YiOHK8+Gd0p5SUALIwL
+  UHwT/bNBMjK2V3LtEIoPH0PJ5MHr1k6foEBYuEblfp53IMwdKFKsZHaSuSES7S3W
+  tj/+Yw/K4Y6mipm356Ke6wKBgQC6tvFwuRa98EOYN2fjD4A1W1tN8f2GINUPKoSQ
+  iinuNIN9I3xKG4pRbfk2XL2y1pm8xqZAq9EyRCCEz9LHtKpVNXmNxArbkf73r1wK
+  nLqem6RKq4GcF9RWIsmJ/QmWMiTlG+4YeeumkqDCfdr/fT5/qLZAFgZsysadp7FQ
+  WOg76QKBgQCrDvcFaCVM+GipRyxaOG+TZttAoaaFTrhVrZbEPIH1rP+7aTbFTZt0
+  Sm37XdDoRlnUtF1CbLWSEeBsGZ2qIiQQ4MKcwU4Bw+Pp4wKpe7sRBrDeZAzbVOqe
+  zSZPRlOta72qhsE+lDeks63CRZpuEXYvQOXqgVxGGMoUzJZ1U1VdVg==
+  -----END RSA PRIVATE KEY-----
+PEM
+
+key_id = "a937ba2a-7b67-4903-9355-ae90f6bf015d"
+base_url = "https://payment-api-sandbox.starlingbank.com"
+faraday ||= Faraday.new(base_url, _connection_opts = {}) do |conn|
+  conn.request :json # JSON has to be serialized before the request gets signed
+  conn.request :starling_request_signing, private_key: private_key, key_id: key_id
+  conn.response :json, parser_options: {symbolize_names: true}
+end
+
+response = faraday.get("/api/v1/7d0b3a0a-f0f9-4579-b7fa-9c091d243d48")
+warn response.status
+warn response.body