Add credential helper support for private gem registries

rubygems/rfcs#59

Author: atpons

bundler/lib/bundler/settings.rb

@@ -89,6 +89,7 @@ class Settings
       system_bindir
       trust-policy
       version
+      credential-helper
     ].freeze
 
     DEFAULT_CONFIG = {
@@ -197,7 +198,7 @@ def mirror_for(uri)
     end
 
     def credentials_for(uri)
-      self[uri.to_s] || self[uri.host]
+      credentials_from_helper(uri) || self[uri.to_s] || self[uri.host]
     end
 
     def gem_mirrors
@@ -595,5 +596,18 @@ def self.key_to_s(key)
         end
       end
     end
+
+    def credentials_from_helper(uri)
+      helper_key = "credential-helper.#{uri.host}"
+      helper_path = self[helper_key]
+      return unless helper_path
+
+      begin
+        output = `#{helper_path}`.strip
+        output unless output.empty?
+      rescue StandardError => e
+        Bundler.ui.warn "Credential helper failed: #{e.message}"
+      end
+    end
   end
 end

bundler/spec/bundler/settings_spec.rb

@@ -263,6 +263,31 @@
         expect(settings.credentials_for(uri)).to eq(credentials)
       end
     end
+
+    context "with credential helper configured" do
+      let(:helper_path) { "/path/to/helper" }
+
+      before do
+        settings.set_local "credential-helper.gemserver.example.org", helper_path
+      end
+
+      it "uses the credential helper when configured" do
+        expect(settings).to receive(:`).with(helper_path).and_return("username:password\n")
+        expect(settings.credentials_for(uri)).to eq("username:password")
+      end
+
+      it "fallback to config when helper fails" do
+        expect(settings).to receive(:`).with(helper_path).and_raise(StandardError, "Helper failed")
+        expect(Bundler.ui).to receive(:warn).with("Credential helper failed: Helper failed")
+        settings.set_local "gemserver.example.org", "fallback:password"
+        expect(settings.credentials_for(uri)).to eq("fallback:password")
+      end
+
+      it "returns nil when helper fails and no fallback config exists" do
+        expect(settings).to receive(:`).with(helper_path).and_return("")
+        expect(settings.credentials_for(uri)).to be_nil
+      end
+    end
   end
 
   describe "URI normalization" do