acme: preserve account URI on get and update

Let's Encrypt has always provided Account URI in a response
to any registration request (new, get and update) in the Location
header, up until recently (?).

Today, LE's servers provide Account URI only for new-reg requests.
In fact, the spec does not say anything about Account URI and Location
header for "get" and "update" requests.

This change preserves Account URI in return values for "get" and "update"
requests, which is already provided by the caller anyway.

Change-Id: I8b1112d7443935715e9184a511b5e30a27008e8c
Reviewed-on: https://go-review.googlesource.com/26931
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

acme/internal/acme/acme.go

@@ -229,14 +229,24 @@ func (c *Client) Register(a *Account, prompt func(tos string) bool) (*Account, e
 // GetReg retrieves an existing registration.
 // The url argument is an Account URI.
 func (c *Client) GetReg(url string) (*Account, error) {
-	a := &Account{URI: url}
-	return c.doReg(url, "reg", a)
+	a, err := c.doReg(url, "reg", nil)
+	if err != nil {
+		return nil, err
+	}
+	a.URI = url
+	return a, nil
 }
 
 // UpdateReg updates an existing registration.
 // It returns an updated account copy. The provided account is not modified.
 func (c *Client) UpdateReg(a *Account) (*Account, error) {
-	return c.doReg(a.URI, "reg", a)
+	uri := a.URI
+	a, err := c.doReg(uri, "reg", a)
+	if err != nil {
+		return nil, err
+	}
+	a.URI = uri
+	return a, nil
 }
 
 // Authorize performs the initial step in an authorization flow.

acme/internal/acme/acme_test.go

@@ -205,6 +205,9 @@ func TestUpdateReg(t *testing.T) {
 	if a.CurrentTerms != terms {
 		t.Errorf("a.CurrentTerms = %q; want %q", a.CurrentTerms, terms)
 	}
+	if a.URI != ts.URL {
+		t.Errorf("a.URI = %q; want %q", a.URI, ts.URL)
+	}
 }
 
 func TestGetReg(t *testing.T) {
@@ -266,6 +269,9 @@ func TestGetReg(t *testing.T) {
 	if a.CurrentTerms != newTerms {
 		t.Errorf("a.CurrentTerms = %q; want %q", a.CurrentTerms, newTerms)
 	}
+	if a.URI != ts.URL {
+		t.Errorf("a.URI = %q; want %q", a.URI, ts.URL)
+	}
 }
 
 func TestAuthorize(t *testing.T) {