diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..24acb65
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,24 @@
+google_auth_proxy
+# Go.gitignore
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
diff --git a/README.md b/README.md
index 8e8ef74..94fdcb3 100644
--- a/README.md
+++ b/README.md
@@ -28,12 +28,19 @@ individual accounts, or a whole google apps domain.
 ## Usage
 
 ```
-./google_auth_proxy
+Usage of ./google_auth_proxy:
+  -authenticated-emails-file="": authenticate against emails via file (one per line)
   -client-id="": the Google OAuth Client ID: ie: "123456.apps.googleusercontent.com"
-  -client-secret="": the OAuth Client secret
-  -cookie-secret="": the seed for cookie values
-  -redirect-url="": the http base to redirect to. ie: https://internalapp.yourcompany.com/oauth2/callback
-  -htpasswd-file="": additionally lookup basic auth in a htpasswd file. Entries must be created with "htpasswd -s" for SHA encryption
-  -pass-basic-auth=true: pass basic auth information to upstream
-  -upstream=[]: the http url(s) of the upstream endpoint(s). If multiple, routing is based on URL path
-```
\ No newline at end of file
+  -client-secret="": the OAuth Client Secret
+  -cookie-domain="": an optional cookie domain to force cookies to
+  -cookie-secret="": the seed string for secure cookies
+  -google-apps-domain="": authenticate against the given google apps domain
+  -htpasswd-file="": additionally authenticate against a htpasswd file. Entries must be created with "htpasswd -s" for SHA encryption
+  -http-address="0.0.0.0:4180": <addr>:<port> to listen on for HTTP clients
+  -pass-basic-auth=true: pass HTTP Basic Auth information to upstream
+  -redirect-url="": the OAuth Redirect URL. ie: "https://internalapp.yourcompany.com/oauth2/callback"
+  -upstream=[]: the http url(s) of the upstream endpoint. If multiple, routing is based on path
+  -version=false: print version string
+```
+
+Unauthenticated requests will be redirected to `/oauth2/sign_in` to start the sign-in process.
diff --git a/cookies.go b/cookies.go
new file mode 100644
index 0000000..1faf480
--- /dev/null
+++ b/cookies.go
@@ -0,0 +1,50 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/sha1"
+	"encoding/base64"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func validateCookie(cookie *http.Cookie, seed string) (string, bool) {
+	// value, timestamp, sig
+	parts := strings.Split(cookie.Value, "|")
+	if len(parts) != 3 {
+		return "", false
+	}
+	sig := cookieSignature(seed, cookie.Name, parts[0], parts[1])
+	if parts[2] == sig {
+		ts, err := strconv.Atoi(parts[1])
+		if err == nil && int64(ts) > time.Now().Add(time.Duration(24)*7*time.Hour*-1).Unix() {
+			// it's a valid cookie. now get the contents
+			rawValue, err := base64.URLEncoding.DecodeString(parts[0])
+			if err == nil {
+				return string(rawValue), true
+			}
+		}
+	}
+	return "", false
+}
+
+func signedCookieValue(seed string, key string, value string) string {
+	encodedValue := base64.URLEncoding.EncodeToString([]byte(value))
+	timeStr := fmt.Sprintf("%d", time.Now().Unix())
+	sig := cookieSignature(seed, key, encodedValue, timeStr)
+	cookieVal := fmt.Sprintf("%s|%s|%s", encodedValue, timeStr, sig)
+	return cookieVal
+}
+
+func cookieSignature(args ...string) string {
+	h := hmac.New(sha1.New, []byte(args[0]))
+	for _, arg := range args[1:] {
+		h.Write([]byte(arg))
+	}
+	var b []byte
+	b = h.Sum(b)
+	return base64.URLEncoding.EncodeToString(b)
+}
diff --git a/htpasswd.go b/htpasswd.go
new file mode 100644
index 0000000..8525c71
--- /dev/null
+++ b/htpasswd.go
@@ -0,0 +1,55 @@
+package main
+
+import (
+	"crypto/sha1"
+	"encoding/base64"
+	"encoding/csv"
+	"log"
+	"os"
+)
+
+// lookup passwords in a htpasswd file
+// The entries must have been created with -s for SHA encryption
+
+type HtpasswdFile struct {
+	Users map[string]string
+}
+
+func NewHtpasswdFile(path string) *HtpasswdFile {
+	log.Printf("using htpasswd file %s", path)
+	r, err := os.Open(path)
+	if err != nil {
+		log.Fatalf("failed opening %v, %s", path, err.Error())
+	}
+	csv_reader := csv.NewReader(r)
+	csv_reader.Comma = ':'
+	csv_reader.Comment = '#'
+	csv_reader.TrimLeadingSpace = true
+
+	records, err := csv_reader.ReadAll()
+	if err != nil {
+		log.Fatalf("Failed reading file %s", err.Error())
+	}
+	h := &HtpasswdFile{Users: make(map[string]string)}
+	for _, record := range records {
+		h.Users[record[0]] = record[1]
+	}
+	return h
+}
+
+func (h *HtpasswdFile) Validate(user string, password string) bool {
+	realPassword, exists := h.Users[user]
+	if !exists {
+		return false
+	}
+	if realPassword[:5] == "{SHA}" {
+		d := sha1.New()
+		d.Write([]byte(password))
+		if realPassword[5:] == base64.StdEncoding.EncodeToString(d.Sum(nil)) {
+			return true
+		}
+	} else {
+		log.Printf("Invalid htpasswd entry for %s. Must be a SHA entry.", user)
+	}
+	return false
+}
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..92726ad
--- /dev/null
+++ b/main.go
@@ -0,0 +1,90 @@
+package main
+
+import (
+	"flag"
+	"log"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"fmt"
+)
+
+const VERSION = "0.0.1"
+
+var (
+	showVersion             = flag.Bool("version", false, "print version string")
+	httpAddr                = flag.String("http-address", "0.0.0.0:4180", "<addr>:<port> to listen on for HTTP clients")
+	redirectUrl             = flag.String("redirect-url", "", "the OAuth Redirect URL. ie: \"https://internalapp.yourcompany.com/oauth2/callback\"")
+	clientID                = flag.String("client-id", "", "the Google OAuth Client ID: ie: \"123456.apps.googleusercontent.com\"")
+	clientSecret            = flag.String("client-secret", "", "the OAuth Client Secret")
+	passBasicAuth           = flag.Bool("pass-basic-auth", true, "pass HTTP Basic Auth information to upstream")
+	htpasswdFile            = flag.String("htpasswd-file", "", "additionally authenticate against a htpasswd file. Entries must be created with \"htpasswd -s\" for SHA encryption")
+	cookieSecret            = flag.String("cookie-secret", "", "the seed string for secure cookies")
+	cookieDomain            = flag.String("cookie-domain", "", "an optional cookie domain to force cookies to")
+	googleAppsDomain        = flag.String("google-apps-domain", "", "authenticate against the given google apps domain")
+	authenticatedEmailsFile = flag.String("authenticated-emails-file", "", "authenticate against emails via file (one per line)")
+	upstreams               = StringArray{}
+)
+
+func init() {
+	flag.Var(&upstreams, "upstream", "the http url(s) of the upstream endpoint. If multiple, routing is based on path")
+}
+
+func main() {
+	flag.Parse()
+
+	if *showVersion {
+		fmt.Printf("google_auth_proxy v%s\n", VERSION)
+		return
+	}
+
+	if len(upstreams) < 1 {
+		log.Fatal("missing --upstream")
+	}
+	if *cookieSecret == "" {
+		log.Fatal("missing --cookie-secret")
+	}
+	if *clientID == "" {
+		log.Fatal("missing --client-id")
+	}
+	if *clientSecret == "" {
+		log.Fatal("missing --client-secret")
+	}
+
+	var upstreamUrls []*url.URL
+	for _, u := range upstreams {
+		upstreamUrl, err := url.Parse(u)
+		if err != nil {
+			log.Fatalf("error parsing --upstream %s", err.Error())
+		}
+		upstreamUrls = append(upstreamUrls, upstreamUrl)
+	}
+	redirectUrl, err := url.Parse(*redirectUrl)
+	if err != nil {
+		log.Fatalf("error parsing --redirect-url %s", err.Error())
+	}
+
+	validator := NewValidator(*googleAppsDomain, *authenticatedEmailsFile)
+	oauthproxy := NewOauthProxy(upstreamUrls, *clientID, *clientSecret, validator)
+	oauthproxy.SetRedirectUrl(redirectUrl)
+	if *googleAppsDomain != "" && *authenticatedEmailsFile == "" {
+		oauthproxy.SignInMessage = fmt.Sprintf("using a %s email address", *googleAppsDomain)
+	}
+	if *htpasswdFile != "" {
+		oauthproxy.HtpasswdFile = NewHtpasswdFile(*htpasswdFile)
+	}
+	listener, err := net.Listen("tcp", *httpAddr)
+	if err != nil {
+		log.Fatalf("FATAL: listen (%s) failed - %s", *httpAddr, err.Error())
+	}
+	log.Printf("listening on %s", *httpAddr)
+
+	server := &http.Server{Handler: oauthproxy}
+	err = server.Serve(listener)
+	if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
+		log.Printf("ERROR: http.Serve() - %s", err.Error())
+	}
+
+	log.Printf("HTTP: closing %s", listener.Addr().String())
+}
diff --git a/oauthproxy.go b/oauthproxy.go
new file mode 100644
index 0000000..f96adc3
--- /dev/null
+++ b/oauthproxy.go
@@ -0,0 +1,302 @@
+package main
+
+import (
+	"bytes"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"github.com/bitly/go-simplejson"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"strings"
+	"time"
+)
+
+const signInPath = "/oauth2/sign_in"
+const oauthStartPath = "/oauth2/start"
+const oauthCallbackPath = "/oauth2/callback"
+
+type OauthProxy struct {
+	CookieSeed string
+	CookieKey  string
+	Validator  func(string) bool
+
+	redirectUrl        *url.URL // the url to receive requests at
+	oauthRedemptionUrl *url.URL // endpoint to redeem the code
+	oauthLoginUrl      *url.URL // to redirect the user to
+	oauthUserInfoUrl   *url.URL
+	oauthScope         string
+	clientID           string
+	clientSecret       string
+	SignInMessage      string
+	HtpasswdFile       *HtpasswdFile
+	serveMux           *http.ServeMux
+}
+
+func NewOauthProxy(proxyUrls []*url.URL, clientID string, clientSecret string, validator func(string) bool) *OauthProxy {
+	login, _ := url.Parse("https://accounts.google.com/o/oauth2/auth")
+	redeem, _ := url.Parse("https://accounts.google.com/o/oauth2/token")
+	info, _ := url.Parse("https://www.googleapis.com/oauth2/v2/userinfo")
+	serveMux := http.NewServeMux()
+	for _, u := range proxyUrls {
+		path := u.Path
+		u.Path = ""
+		log.Printf("mapping %s => %s", path, u)
+		serveMux.Handle(path, httputil.NewSingleHostReverseProxy(u))
+	}
+	return &OauthProxy{
+		CookieKey:  "_oauthproxy",
+		CookieSeed: *cookieSecret,
+		Validator:  validator,
+
+		clientID:           clientID,
+		clientSecret:       clientSecret,
+		oauthScope:         "https://www.googleapis.com/auth/userinfo.profile https://www.googleapis.com/auth/userinfo.email",
+		oauthRedemptionUrl: redeem,
+		oauthLoginUrl:      login,
+		oauthUserInfoUrl:   info,
+		serveMux:           serveMux,
+	}
+}
+
+func (p *OauthProxy) SetRedirectUrl(redirectUrl *url.URL) {
+	redirectUrl.Path = oauthCallbackPath
+	p.redirectUrl = redirectUrl
+}
+
+func (p *OauthProxy) GetLoginURL() string {
+	params := url.Values{}
+	params.Add("redirect_uri", p.redirectUrl.String())
+	params.Add("approval_prompt", "force")
+	params.Add("scope", p.oauthScope)
+	params.Add("client_id", p.clientID)
+	params.Add("response_type", "code")
+	return fmt.Sprintf("%s?%s", p.oauthLoginUrl, params.Encode())
+}
+
+func apiRequest(req *http.Request) (*simplejson.Json, error) {
+	httpclient := &http.Client{}
+	resp, err := httpclient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	body, err := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != 200 {
+		log.Printf("got response code %d - %s", resp.StatusCode, body)
+		return nil, errors.New("api request returned 200 status code")
+	}
+	data, err := simplejson.NewJson(body)
+	if err != nil {
+		return nil, err
+	}
+	return data, nil
+}
+
+func (p *OauthProxy) redeemCode(code string) (string, error) {
+
+	params := url.Values{}
+	params.Add("redirect_uri", p.redirectUrl.String())
+	params.Add("client_id", p.clientID)
+	params.Add("client_secret", p.clientSecret)
+	params.Add("code", code)
+	params.Add("grant_type", "authorization_code")
+	log.Printf("body is %s", params.Encode())
+	req, err := http.NewRequest("POST", p.oauthRedemptionUrl.String(), bytes.NewBufferString(params.Encode()))
+	if err != nil {
+		log.Printf("failed building request %s", err.Error())
+		return "", err
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	json, err := apiRequest(req)
+	if err != nil {
+		log.Printf("failed making request %s", err.Error())
+		return "", err
+	}
+	access_token, err := json.Get("access_token").String()
+	if err != nil {
+		return "", err
+	}
+	return access_token, nil
+}
+func (p *OauthProxy) getUserInfo(token string) (string, error) {
+	params := url.Values{}
+	params.Add("access_token", token)
+	endpoint := fmt.Sprintf("%s?%s", p.oauthUserInfoUrl.String(), params.Encode())
+	log.Printf("calling %s", endpoint)
+	req, err := http.NewRequest("GET", endpoint, nil)
+	if err != nil {
+		log.Printf("failed building request %s", err.Error())
+		return "", err
+	}
+	json, err := apiRequest(req)
+	if err != nil {
+		log.Printf("failed making request %s", err.Error())
+		return "", err
+	}
+	email, err := json.Get("email").String()
+	if err != nil {
+		log.Printf("failed getting email from response %s", err.Error())
+		return "", err
+	}
+	return email, nil
+}
+
+func ClearCookie(rw http.ResponseWriter, req *http.Request, key string) {
+	domain := strings.Split(req.Host, ":")[0]
+	if *cookieDomain != "" {
+		domain = *cookieDomain
+	}
+	cookie := &http.Cookie{
+		Name:     key,
+		Value:    "",
+		Path:     "/",
+		Domain:   domain,
+		Expires:  time.Now().Add(time.Duration(1) * time.Hour * -1),
+		HttpOnly: true,
+	}
+	http.SetCookie(rw, cookie)
+}
+
+func ErrorPage(rw http.ResponseWriter, code int, title string, message string, signinmessage string) {
+	log.Printf("ErrorPage %d %s %s %s", code, title, message, signinmessage)
+	rw.WriteHeader(code)
+	t := getTemplates()
+	p := struct {
+		Title         string
+		Message       string
+		SignInMessage string
+	}{
+		Title:         fmt.Sprintf("%d %s", code, title),
+		Message:       message,
+		SignInMessage: signinmessage,
+	}
+	t.ExecuteTemplate(rw, "error.html", p)
+}
+
+func (p *OauthProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	// check if this is a redirect back at the end of oauth
+	if req.URL.Path == signInPath {
+		ClearCookie(rw, req, p.CookieKey)
+		t := getTemplates()
+		p := struct{ SignInMessage string }{SignInMessage: p.SignInMessage}
+		t.ExecuteTemplate(rw, "sign_in.html", p)
+		return
+	}
+	if req.URL.Path == oauthStartPath {
+		http.Redirect(rw, req, p.GetLoginURL(), 302)
+		return
+	}
+	if req.URL.Path == oauthCallbackPath {
+		// finish the oauth cycle
+		reqParams, err := url.ParseQuery(req.URL.RawQuery)
+		if err != nil {
+			ErrorPage(rw, 500, "Internal Error", err.Error(), p.SignInMessage)
+			return
+		}
+		errorString, ok := reqParams["error"]
+		if ok && len(errorString) == 1 {
+			ErrorPage(rw, 403, "Permission Denied", errorString[0], p.SignInMessage)
+			return
+		}
+		code, ok := reqParams["code"]
+		if !ok || len(code) != 1 {
+			ErrorPage(rw, 500, "Internal Error", "Invalid API response", p.SignInMessage)
+			return
+		}
+
+		token, err := p.redeemCode(code[0])
+		if err != nil {
+			log.Printf("error redeeming code %s", err.Error())
+			ErrorPage(rw, 500, "Internal Error", err.Error(), p.SignInMessage)
+			return
+		}
+		// validate user
+		email, err := p.getUserInfo(token)
+		if err != nil {
+			log.Printf("error redeeming code %s", err.Error())
+			ErrorPage(rw, 500, "Internal Error", err.Error(), p.SignInMessage)
+			return
+		}
+
+		// set cookie, or deny
+		if p.Validator(email) {
+			log.Printf("authenticating %s completed", email)
+			domain := strings.Split(req.Host, ":")[0]
+			if *cookieDomain != "" {
+				domain = *cookieDomain
+			}
+
+			cookie := &http.Cookie{
+				Name:     p.CookieKey,
+				Value:    signedCookieValue(p.CookieSeed, p.CookieKey, email),
+				Path:     "/",
+				Domain:   domain,
+				Expires:  time.Now().Add(time.Duration(168) * time.Hour), // 7 days
+				HttpOnly: true,
+				// Secure: req. ... ? set if X-Scheme: https ?
+			}
+			http.SetCookie(rw, cookie)
+			http.Redirect(rw, req, "/", 302)
+			return
+		} else {
+			ErrorPage(rw, 403, "Permission Denied", "Invalid Account", p.SignInMessage)
+			return
+		}
+	}
+	cookie, err := req.Cookie(p.CookieKey)
+	var ok bool
+	var email string
+	var user string
+	if err == nil {
+		email, ok = validateCookie(cookie, p.CookieSeed)
+		user = strings.Split(email, "@")[0]
+	}
+
+	if !ok {
+		user, ok = p.CheckBasicAuth(req)
+	}
+
+	if !ok {
+		log.Printf("invalid cookie. redirecting to sign in")
+		// TODO: capture state for which url to redirect to at the end
+		http.Redirect(rw, req, "/oauth2/sign_in", 302)
+		return
+	}
+
+	// At this point, the user is authenticated. proxy normally
+	if *passBasicAuth {
+		req.SetBasicAuth(user, "")
+		req.Header["X-Forwarded-User"] = []string{user}
+	}
+
+	p.serveMux.ServeHTTP(rw, req)
+}
+
+func (p *OauthProxy) CheckBasicAuth(req *http.Request) (string, bool) {
+	if p.HtpasswdFile == nil {
+		return "", false
+	}
+	s := strings.SplitN(req.Header.Get("Authorization"), " ", 2)
+	if len(s) != 2 || s[0] != "Basic" {
+		return "", false
+	}
+	b, err := base64.StdEncoding.DecodeString(s[1])
+	if err != nil {
+		return "", false
+	}
+	pair := strings.SplitN(string(b), ":", 2)
+	if len(pair) != 2 {
+		return "", false
+	}
+	if p.HtpasswdFile.Validate(pair[0], pair[1]) {
+		return pair[0], true
+	}
+	return "", false
+}
diff --git a/string_array.go b/string_array.go
new file mode 100644
index 0000000..2369196
--- /dev/null
+++ b/string_array.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+)
+
+type StringArray []string
+
+func (a *StringArray) Set(s string) error {
+	*a = append(*a, s)
+	return nil
+}
+
+func (a *StringArray) String() string {
+	return fmt.Sprint(*a)
+}
diff --git a/templates.go b/templates.go
new file mode 100644
index 0000000..b76e30b
--- /dev/null
+++ b/templates.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"html/template"
+	"log"
+)
+
+func getTemplates() *template.Template {
+	t, err := template.New("foo").Parse(`{{define "sign_in.html"}}
+<html><head><title>Sign In</title></head>
+	<body>
+	<form method="GET" action="/oauth2/start">
+	<button type="submit">Sign In w/ Google</button>
+	{{.SignInMessage}}
+	</form>
+</body></html>
+{{end}}`)
+	if err != nil {
+		log.Fatalf("failed parsing template %s", err.Error())
+	}
+	t, err = t.Parse(`{{define "error.html"}}
+<html><head><title>{{.Title}}</title></head>
+<body>
+	<h2>{{.Title}}</h2>
+	<p>{{.Message}}</p>
+	<hr>
+	<form method="GET" action="/oauth2/start">
+	<button type="submit">Sign In w/ Google</button>
+	{{.SignInMessage}}
+	</form>
+</body>
+</html>{{end}}`)
+	if err != nil {
+		log.Fatalf("failed parsing template %s", err.Error())
+	}
+	return t
+}
diff --git a/validator.go b/validator.go
new file mode 100644
index 0000000..178ac50
--- /dev/null
+++ b/validator.go
@@ -0,0 +1,46 @@
+package main
+
+import (
+	"os"
+	"log"
+	"encoding/csv"
+	"fmt"
+	"strings"
+)
+
+func NewValidator(domain string, usersFile string) func(string) bool {
+
+	validUsers := make(map[string]bool)
+	emailSuffix := ""
+	if domain != "" {
+		emailSuffix = fmt.Sprintf("@%s", domain)
+	}
+
+	if usersFile != "" {
+		r, err := os.Open(usersFile)
+		if err != nil {
+			log.Fatalf("failed opening -authenticated-emails-file=%v, %s", usersFile, err.Error())
+		}
+		csv_reader := csv.NewReader(r)
+		csv_reader.Comma = ','
+		csv_reader.Comment = '#'
+		csv_reader.TrimLeadingSpace = true
+		records, err := csv_reader.ReadAll()
+		for _, r := range records {
+			validUsers[r[0]] = true
+		}
+	}
+
+	validator := func(email string) bool {
+		var valid bool
+		if emailSuffix != "" {
+			valid = strings.HasSuffix(email, emailSuffix)
+		}
+		if !valid {
+			_, valid = validUsers[email]
+		}
+		log.Printf("validating: is %s valid? %v", email, valid)
+		return valid
+	}
+	return validator
+}