Add challenge page parser util

http.go

@@ -70,6 +70,21 @@ func NewChallenge(ctx context.Context, hc http.Client, host string) (Challenge,
 	return c, nil
 }
 
+func ParseChallenge(r io.Reader, host string) (Challenge, error) {
+	u, err := parseHost(host)
+	if err != nil {
+		return Challenge{}, err
+	}
+
+	c, err := parseTags(r)
+	if err != nil {
+		return Challenge{}, err
+	}
+	c.host = u
+
+	return c, nil
+}
+
 // Submit a Solution for a Challenge.
 //
 // If redirect is empty, "/" is used as a sensible default.
@@ -137,8 +152,7 @@ func postSolution(ctx context.Context, hc http.Client, s Solution) (*http.Respon
 	// TODO: Additionally verify failure from response JSON. Maybe include resp body in err type.
 	// Rejected solution response: status=400 body={"success":false,"reason":"invalid_solution","action":"retry"}
 	if resp.StatusCode == 400 {
-		defer resp.Body.Close()
-		return nil, &ErrInvalidSolution{s}
+		return resp, &ErrInvalidSolution{s}
 	}
 
 	return resp, nil