Add API endpoint to get a commit's GPG signature

lib/api/commits.rb

@@ -323,6 +323,22 @@ module API
 
         present paginate(commit.merge_requests), with: Entities::MergeRequestBasic
       end
+
+      desc "Get a commit's GPG signature" do
+        success Entities::CommitSignature
+      end
+      params do
+        requires :sha, type: String, desc: 'A commit sha, or the name of a branch or tag'
+      end
+      get ':id/repository/commits/:sha/signature', requirements: API::COMMIT_ENDPOINT_REQUIREMENTS do
+        commit = user_project.commit(params[:sha])
+        not_found! 'Commit' unless commit
+
+        signature = commit.signature
+        not_found! 'GPG Signature' unless signature
+
+        present signature, with: Entities::CommitSignature
+      end
     end
   end
 end

lib/api/entities.rb

@@ -392,6 +392,13 @@ module API
       expose :project_id
     end
 
+    class CommitSignature < Grape::Entity
+      expose :gpg_key_id
+      expose :gpg_key_primary_keyid, :gpg_key_user_name, :gpg_key_user_email
+      expose :verification_status
+      expose :gpg_key_subkey_id
+    end
+
     class BasicRef < Grape::Entity
       expose :type, :name
     end