Add haveibeenpwned sample function

Idea from Matthew Holt, using the haveibeenpwned API to query
whether a password has been found in a data-breach.

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

sample-functions/haveibeenpwned/handler.go

@@ -0,0 +1,78 @@
+// Copyright (c) OpenFaaS Author(s) 2018. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+// API source - https://haveibeenpwned.com/API/v2#SearchingPwnedPasswordsByRange
+// Idea from Matthew Holt (@mholt6)
+
+package function
+
+import (
+	"crypto/sha1"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"strconv"
+	"strings"
+)
+
+// Handle a serverless request
+func Handle(payload []byte) string {
+
+	if len(payload) == 0 {
+		return "Enter a number of characters."
+	}
+
+	hashed := fmt.Sprintf("%X", sha1.Sum(payload))
+	prefix := hashed[:5]
+
+	c := http.Client{}
+
+	req, _ := http.NewRequest(http.MethodGet,
+		fmt.Sprintf("https://api.pwnedpasswords.com/range/%s", prefix), nil)
+
+	res, err := c.Do(req)
+	if err != nil {
+		return err.Error()
+	}
+
+	var bytesOut []byte
+	if res.Body != nil {
+		defer res.Body.Close()
+		bytesOut, _ = ioutil.ReadAll(res.Body)
+	}
+
+	passwords := string(bytesOut)
+	foundTimes, findErr := findPassword(passwords, prefix, hashed)
+	if findErr != nil {
+		return findErr.Error()
+	}
+
+	result := result{Found: foundTimes}
+	output, _ := json.Marshal(result)
+	return string(output)
+}
+
+type result struct {
+	Found int `json:"found"`
+}
+
+func findPassword(passwords string, prefix string, hashed string) (int, error) {
+	foundTimes := 0
+
+	for _, passwordLine := range strings.Split(passwords, "\r\n") {
+		if passwordLine != "" {
+			parts := strings.Split(passwordLine, ":")
+
+			if fmt.Sprintf("%s%s", prefix, parts[0]) == hashed {
+				var convErr error
+				foundTimes, convErr = strconv.Atoi(parts[1])
+				if convErr != nil {
+					return 0, fmt.Errorf(`Cannot convert value: "%s", error: "%s"\n`, parts[1], convErr)
+				}
+				break
+			}
+		}
+	}
+	return foundTimes, nil
+}