Refactor the core of the lib (#700)

- Packages
- Isolate code used by the CLI into the package `cmd`
- (experimental) Add e2e tests for HTTP01, TLS-ALPN-01 and DNS-01, use [Pebble](https://github.com/letsencrypt/pebble) and [challtestsrv](https://github.com/letsencrypt/boulder/tree/master/test/challtestsrv) 
- Support non-ascii domain name (punnycode)
- Check all challenges in a predictable order
- No more global exported variables
- Archive revoked certificates
- Fixes revocation for subdomains and non-ascii domains
- Disable pending authorizations
- use pointer for RemoteError/ProblemDetails
- Poll authz URL instead of challenge URL
- The ability for a DNS provider to solve the challenge sequentially
- Check all nameservers in a predictable order
- Option to disable the complete propagation Requirement
- CLI, support for renew with CSR
- CLI, add SAN on renew
- Add command to list certificates.
- Logs every iteration of waiting for the propagation
- update DNSimple client
- update github.com/miekg/dns

acme/api/internal/sender/sender_test.go

@@ -0,0 +1,68 @@
+package sender
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDo_UserAgentOnAllHTTPMethod(t *testing.T) {
+	var ua, method string
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ua = r.Header.Get("User-Agent")
+		method = r.Method
+	}))
+	defer ts.Close()
+
+	doer := NewDoer(http.DefaultClient, "")
+
+	testCases := []struct {
+		method string
+		call   func(u string) (*http.Response, error)
+	}{
+		{
+			method: http.MethodGet,
+			call: func(u string) (*http.Response, error) {
+				return doer.Get(u, nil)
+			},
+		},
+		{
+			method: http.MethodHead,
+			call:   doer.Head,
+		},
+		{
+			method: http.MethodPost,
+			call: func(u string) (*http.Response, error) {
+				return doer.Post(u, strings.NewReader("falalalala"), "text/plain", nil)
+			},
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.method, func(t *testing.T) {
+
+			_, err := test.call(ts.URL)
+			require.NoError(t, err)
+
+			assert.Equal(t, test.method, method)
+			assert.Contains(t, ua, ourUserAgent, "User-Agent")
+		})
+	}
+}
+
+func TestDo_CustomUserAgent(t *testing.T) {
+	customUA := "MyApp/1.2.3"
+	doer := NewDoer(http.DefaultClient, customUA)
+
+	ua := doer.formatUserAgent()
+	assert.Contains(t, ua, ourUserAgent)
+	assert.Contains(t, ua, customUA)
+	if strings.HasSuffix(ua, " ") {
+		t.Errorf("UA should not have trailing spaces; got '%s'", ua)
+	}
+	assert.Len(t, strings.Split(ua, " "), 5)
+}