Support setting SSL client cert as a an array, to configure extra_chain_cert

lib/faraday/adapter/net_http.rb

@@ -133,7 +133,10 @@ def configure_ssl(http, ssl)
         http.verify_mode = ssl_verify_mode(ssl)
         http.cert_store = ssl_cert_store(ssl)
 
-        http.cert = ssl[:client_cert] if ssl[:client_cert]
+        cert, *extra_chain_cert = ssl[:client_cert]
+        http.cert = cert if cert
+        http.extra_chain_cert = extra_chain_cert if extra_chain_cert.any?
+
         http.key = ssl[:client_key] if ssl[:client_key]
         http.ca_file = ssl[:ca_file] if ssl[:ca_file]
         http.ca_path = ssl[:ca_path] if ssl[:ca_path]

spec/faraday/adapter/net_http_spec.rb

@@ -147,4 +147,48 @@
       it { expect(response.body.encoding).to eq(::Encoding::UTF_8) }
     end
   end
+
+  context 'client certificate' do
+    let(:adapter) { described_class.new }
+    let(:url) { URI('https://example.com') }
+    let(:http) { adapter.send(:connection, url: url, request: {}, ssl: ssl_options) }
+
+    before do
+      stub_request(:any, 'https://example.com')
+    end
+
+    context 'when client_cert is provided as an array' do
+      let(:cert_array) { [OpenSSL::X509::Certificate.new, OpenSSL::X509::Certificate.new] }
+      let(:ssl_options) do
+        Faraday::SSLOptions.new.tap do |ssl_options|
+          ssl_options.client_cert = cert_array
+        end
+      end
+
+      it 'sets the first cert as cert and the rest as extra_chain_cert' do
+        adapter.send(:configure_ssl, http, ssl_options)
+      end
+
+      it { expect(http.cert).to eq(cert_array.first) }
+
+      it { expect(http.extra_chain_cert).to eq(cert_array[1..]) }
+    end
+
+    context 'when client_cert is provided as a single cert' do
+      let(:cert) { OpenSSL::X509::Certificate.new }
+      let(:ssl_options) do
+        Faraday::SSLOptions.new.tap do |ssl_options|
+          ssl_options.client_cert = cert
+        end
+      end
+
+      it 'sets the cert as cert' do
+        adapter.send(:configure_ssl, http, ssl_options)
+      end
+
+      it { expect(http.cert).to eq(cert) }
+
+      it { expect(http.extra_chain_cert).to be_nil }
+    end
+  end
 end