Add Universign timestamp API query

app/lib/universign/api.rb

@@ -0,0 +1,40 @@
+class Universign::API
+  ## Universign Timestamp POST API
+  # Official documentation is at https://help.universign.com/hc/fr/articles/360000898965-Guide-d-intégration-horodatage
+
+  def self.ensure_properly_configured!
+    if userpwd.blank?
+      raise StandardError, 'Universign API is not properly configured'
+    end
+  end
+
+  def self.timestamp(data)
+    ensure_properly_configured!
+
+    response = Typhoeus.post(
+      UNIVERSIGN_API_URL,
+      userpwd: userpwd,
+      body: body(data)
+    )
+
+    if response.success?
+      response.body
+    else
+      raise StandardError, "Universign timestamp query failed: #{response.status_message}"
+    end
+  end
+
+  private
+
+  def self.body(data)
+    {
+      'hashAlgo': 'SHA256',
+      'withCert': 'true',
+      'hashValue': data
+    }
+  end
+
+  def self.userpwd
+    Rails.application.secrets.universign[:userpwd]
+  end
+end