Validates that user is a human.

Add google recaptcha as an initial page before creating any session.
To configure recaptcha there are 2 environment variables that are needed
`GOOGLE_RECAPTCHA_SITE_KEY` and `GOOGLE_RECAPTCHA_SITE_SECRET`.
The code contains development defaults that should be set in production
to real values.
**NOTICE: Development defaults assume that the domain is `localhost`**

api.go

@@ -7,12 +7,18 @@ import (
 
 	"github.com/franela/play-with-docker/handlers"
 	"github.com/franela/play-with-docker/services"
+	"github.com/franela/play-with-docker/templates"
 	"github.com/gorilla/mux"
 	"github.com/urfave/negroni"
 )
 
 func main() {
 
+	welcome, tmplErr := templates.GetWelcomeTemplate()
+	if tmplErr != nil {
+		log.Fatal(tmplErr)
+	}
+
 	server := services.CreateWSServer()
 
 	server.On("connection", handlers.WS)
@@ -27,7 +33,11 @@ func main() {
 	r.StrictSlash(false)
 
 	r.HandleFunc("/ping", http.HandlerFunc(handlers.Ping)).Methods("GET")
-	r.HandleFunc("/", http.HandlerFunc(handlers.NewSession)).Methods("GET")
+	r.HandleFunc("/", http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		rw.Write(welcome)
+	})).Methods("GET")
+	r.HandleFunc("/", http.HandlerFunc(handlers.NewSession)).Methods("POST")
+
 	r.HandleFunc("/sessions/{sessionId}", http.HandlerFunc(handlers.GetSession)).Methods("GET")
 	r.HandleFunc("/sessions/{sessionId}/instances", http.HandlerFunc(handlers.NewInstance)).Methods("POST")
 	r.HandleFunc("/sessions/{sessionId}/instances/{instanceName}", http.HandlerFunc(handlers.DeleteInstance)).Methods("DELETE")

handlers/new_session.go

@@ -9,6 +9,13 @@ import (
 )
 
 func NewSession(rw http.ResponseWriter, req *http.Request) {
+	if !services.IsHuman(req) {
+		// User it not a human
+		rw.WriteHeader(http.StatusConflict)
+		rw.Write([]byte("Only humans are allowed!"))
+		return
+	}
+
 	s, err := services.NewSession()
 	if err != nil {
 		log.Println(err)

services/recaptcha.go

@@ -0,0 +1,59 @@
+package services
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+)
+
+func GetGoogleRecaptchaSiteKey() string {
+	key := os.Getenv("GOOGLE_RECAPTCHA_SITE_KEY")
+	if key == "" {
+		// This is a development default. The environment variable should always be set in production.
+		key = "6LeY_QsUAAAAAOlpVw4MhoLEr50h-dM80oz6M2AX"
+	}
+	return key
+}
+func GetGoogleRecaptchaSiteSecret() string {
+	key := os.Getenv("GOOGLE_RECAPTCHA_SITE_SECRET")
+	if key == "" {
+		// This is a development default. The environment variable should always be set in production.
+		key = "6LeY_QsUAAAAAHIALCtm0GKfk-UhtXoyJKarnRV8"
+	}
+
+	return key
+}
+
+type recaptchaResponse struct {
+	Success bool `json:"success"`
+}
+
+func IsHuman(req *http.Request) bool {
+	req.ParseForm()
+	challenge := req.Form.Get("g-recaptcha-response")
+
+	// Of X-Forwarded-For exists, it means we are behind a loadbalancer and we should use the real IP address of the user
+	ip := req.Header.Get("X-Forwarded-For")
+	if ip == "" {
+		// Use the standard remote IP address of the request
+
+		ip = req.RemoteAddr
+	}
+
+	parts := strings.Split(ip, ":")
+
+	resp, postErr := http.PostForm("https://www.google.com/recaptcha/api/siteverify", url.Values{"secret": {GetGoogleRecaptchaSiteSecret()}, "response": {challenge}, "remoteip": {parts[0]}})
+	if postErr != nil {
+		log.Println(postErr)
+		// If there is a problem to connect to google, assume the user is a human so we don't block real users because of technical issues
+		return true
+	}
+
+	var r recaptchaResponse
+	json.NewDecoder(resp.Body).Decode(&r)
+
+	return r.Success
+}

templates/welcome.go

@@ -0,0 +1,21 @@
+package templates
+
+import (
+	"bytes"
+	"html/template"
+
+	"github.com/franela/play-with-docker/services"
+)
+
+func GetWelcomeTemplate() ([]byte, error) {
+	welcomeTemplate, tplErr := template.New("welcome").ParseFiles("www/welcome.html")
+	if tplErr != nil {
+		return nil, tplErr
+	}
+	var b bytes.Buffer
+	tplExecuteErr := welcomeTemplate.ExecuteTemplate(&b, "GOOGLE_RECAPTCHA_SITE_KEY", services.GetGoogleRecaptchaSiteKey())
+	if tplExecuteErr != nil {
+		return nil, tplExecuteErr
+	}
+	return b.Bytes(), nil
+}

www/assets/style.css

@@ -27,3 +27,18 @@ md-card-content.terminal {
     color: #1da4eb;
     text-align: center;
 }
+
+.welcome {
+    background-color: #e7e7e7;
+}
+
+.welcome > div {
+    text-align: center;
+}
+
+.g-recaptcha div {
+    margin-left: auto;
+    margin-right: auto;
+    margin-bottom: auto;
+    margin-top: 50px;
+}

www/welcome.html

@@ -0,0 +1,27 @@
+{{define "GOOGLE_RECAPTCHA_SITE_KEY"}}
+<!doctype html>
+<html ng-app="DockerPlay" ng-controller="PlayController">
+    <head>
+        <title>Docker Playground</title>
+	    <link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/angular_material/1.1.0/angular-material.min.css">
+        <link rel="stylesheet" href="/assets/style.css" />
+        <script src='https://www.google.com/recaptcha/api.js'></script>
+    </head>
+    <body class="welcome">
+        <div>
+            <h1>Welcome!</h1>
+            <h2>Before starting we need to verify you are a human</h2>
+            <form id="welcomeForm" method="POST" action="/">
+                <div class="g-recaptcha" data-callback="iAmHuman" data-sitekey="{{.}}"></div>
+            </form>
+            <img src="/assets/large_h.png" />
+        </div>
+
+        <script>
+            function iAmHuman(resp) {
+                document.getElementById('welcomeForm').submit();
+            }
+        </script>
+    </body>
+</html>
+{{end}}