feature: trusted ip address ranges skip authentication (#4)

Co-authored-by: Alexander Metzner <alexander.metzner@nortal.com>

README.md

@@ -166,6 +166,7 @@ Application Options:
   --whitelist=                                          Only allow given user ID, comma separated, can be set multiple times [$WHITELIST]
   --port=                                               Port to listen on (default: 4181) [$PORT]
   --rule.<name>.<param>=                                Rule definitions, param can be: "action", "rule" or "provider"
+  --trusted-ip-address=                                 List of trusted IP addresses or IP networks (in CIDR notation) that are considered authenticated [$TRUSTED_IP_ADDRESS]  
 
 Google Provider:
   --providers.google.client-id=                         Client ID [$PROVIDERS_GOOGLE_CLIENT_ID]
@@ -362,6 +363,17 @@ All options can be supplied in any of the following ways, in the following prece
 
    Note: It is possible to break your redirect flow with rules, please be careful not to create an `allow` rule that matches your redirect_uri unless you know what you're doing. This limitation is being tracked in in #101 and the behaviour will change in future releases.
 
+- `trusted-ip-address`
+
+  This option adds an IP address or an IP network given in CIDR notation to the list of trusted networks. Requests originating
+  from a trusted network are considered authenticated and are never redirected to an OAuth IDP. The option can be used
+  multiple times to add many trusted address ranges.
+
+  * `--trusted-ip-address=2.3.4.5` adds a single IP (`2.3.4.5`) as a trusted IP.
+  * `--trusted-ip-address=30.1.0.0/16` adds the address range from `30.1.0.1` to `30.1.255.254` as a trusted range
+
+  The list of trusted networks is initially empty.
+
 ## Concepts
 
 ### User Restriction

internal/config.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"net"
 	"os"
 	"regexp"
 	"strconv"
@@ -56,6 +57,9 @@ type Config struct {
 	ClientIdLegacy      string        `long:"client-id" env:"CLIENT_ID" description:"DEPRECATED - Use \"providers.google.client-id\""`
 	ClientSecretLegacy  string        `long:"client-secret" env:"CLIENT_SECRET" description:"DEPRECATED - Use \"providers.google.client-id\""  json:"-"`
 	PromptLegacy        string        `long:"prompt" env:"PROMPT" description:"DEPRECATED - Use \"providers.google.prompt\""`
+
+	TrustedIPAddresses []string `long:"trusted-ip-address" env:"TRUSTED_IP_ADDRESS" env-delim:"," description:"List of trusted IP addresses or IP networks (in CIDR notation) that are considered authenticated"`
+	trustedIPNetworks  []*net.IPNet
 }
 
 // NewGlobalConfig creates a new global config, parsed from command arguments
@@ -131,9 +135,41 @@ func NewConfig(args []string) (*Config, error) {
 	c.Secret = []byte(c.SecretString)
 	c.Lifetime = time.Second * time.Duration(c.LifetimeString)
 
+	if err := c.parseTrustedNetworks(); err != nil {
+		return nil, err
+	}
+
 	return c, nil
 }
 
+func (c *Config) parseTrustedNetworks() error {
+	c.trustedIPNetworks = make([]*net.IPNet, len(c.TrustedIPAddresses))
+
+	for i := range c.TrustedIPAddresses {
+		addr := c.TrustedIPAddresses[i]
+		if strings.Contains(addr, "/") {
+			_, net, err := net.ParseCIDR(addr)
+			if err != nil {
+				return err
+			}
+			c.trustedIPNetworks[i] = net
+			continue
+		}
+
+		ipAddr := net.ParseIP(addr)
+		if ipAddr == nil {
+			return fmt.Errorf("invalid ip address: '%s'", ipAddr)
+		}
+
+		c.trustedIPNetworks[i] = &net.IPNet{
+			IP:   ipAddr,
+			Mask: []byte{255, 255, 255, 255},
+		}
+	}
+
+	return nil
+}
+
 func (c *Config) parseFlags(args []string) error {
 	p := flags.NewParser(c, flags.Default|flags.IniUnknownOptionHandler)
 	p.UnknownOptionHandler = c.parseUnknownFlag
@@ -303,6 +339,22 @@ func (c *Config) GetConfiguredProvider(name string) (provider.Provider, error) {
 	return c.GetProvider(name)
 }
 
+//
+func (c *Config) IsIPAddressAuthenticated(address string) (bool, error) {
+	addr := net.ParseIP(address)
+	if addr == nil {
+		return false, fmt.Errorf("invalid ip address: '%s'", address)
+	}
+
+	for _, n := range c.trustedIPNetworks {
+		if n.Contains(addr) {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
 func (c *Config) providerConfigured(name string) bool {
 	// Check default provider
 	if name == c.DefaultProvider {

internal/config_test.go

@@ -40,6 +40,8 @@ func TestConfigDefaults(t *testing.T) {
 	assert.Equal(c.Port, 4181)
 
 	assert.Equal("select_account", c.Providers.Google.Prompt)
+
+	assert.Len(c.TrustedIPAddresses, 0)
 }
 
 func TestConfigParseArgs(t *testing.T) {
@@ -420,3 +422,31 @@ func TestConfigCommaSeparatedList(t *testing.T) {
 	assert.Nil(err)
 	assert.Equal("one,two", marshal, "should marshal back to comma sepearated list")
 }
+
+func TestConfigTrustedNetworks(t *testing.T) {
+	assert := assert.New(t)
+
+	c, err := NewConfig([]string{
+		"--trusted-ip-address=1.2.3.4",
+		"--trusted-ip-address=30.1.0.0/16",
+	})
+
+	assert.NoError(err)
+
+	table := map[string]bool{
+		"1.2.3.3":      false,
+		"1.2.3.4":      true,
+		"1.2.3.5":      false,
+		"192.168.1.1":  false,
+		"30.1.0.1":     true,
+		"30.1.255.254": true,
+		"30.2.0.1":     false,
+	}
+
+	for in, want := range table {
+		got, err := c.IsIPAddressAuthenticated(in)
+		assert.NoError(err)
+		assert.Equal(want, got, "ip address: %s", in)
+	}
+
+}

internal/server.go

@@ -86,6 +86,20 @@ func (s *Server) AuthHandler(providerName, rule string) http.HandlerFunc {
 		// Logging setup
 		logger := s.logger(r, "Auth", rule, "Authenticating request")
 
+		ipAddr := r.Header.Get("X-Forwarded-For")
+		if ipAddr == "" {
+			logger.Warn("missing x-forwarded-for header")
+		} else {
+			ok, err := config.IsIPAddressAuthenticated(ipAddr)
+			if err != nil {
+				logger.WithField("error", err).Warn("Invalid forwarded for")
+			} else if ok {
+				logger.WithField("addr", ipAddr).Info("Authenticated remote address")
+				w.WriteHeader(200)
+				return
+			}
+		}
+
 		// Get auth cookie
 		c, err := r.Cookie(config.CookieName)
 		if err != nil {

internal/server_test.go

@@ -160,6 +160,42 @@ func TestServerAuthHandlerValid(t *testing.T) {
 	assert.Equal([]string{"test@example.com"}, users, "X-Forwarded-User header should match user")
 }
 
+func TestServerAuthHandlerTrustedIP_trusted(t *testing.T) {
+	assert := assert.New(t)
+	config = newDefaultConfig()
+
+	// Should allow valid request email
+	req := newHTTPRequest("GET", "http://example.com/foo")
+	req.Header.Set("X-Forwarded-For", "127.0.0.2")
+
+	res, _ := doHttpRequest(req, nil)
+	assert.Equal(200, res.StatusCode, "trusted ip should be allowed")
+}
+
+func TestServerAuthHandlerTrustedIP_notTrusted(t *testing.T) {
+	assert := assert.New(t)
+	config = newDefaultConfig()
+
+	// Should allow valid request email
+	req := newHTTPRequest("GET", "http://example.com/foo")
+	req.Header.Set("X-Forwarded-For", "127.0.0.1")
+
+	res, _ := doHttpRequest(req, nil)
+	assert.Equal(307, res.StatusCode, "untrusted ip should not be allowed")
+}
+
+func TestServerAuthHandlerTrustedIP_invalidAddress(t *testing.T) {
+	assert := assert.New(t)
+	config = newDefaultConfig()
+
+	// Should allow valid request email
+	req := newHTTPRequest("GET", "http://example.com/foo")
+	req.Header.Set("X-Forwarded-For", "127.0")
+
+	res, _ := doHttpRequest(req, nil)
+	assert.Equal(307, res.StatusCode, "invalid ip should not be allowed")
+}
+
 func TestServerAuthCallback(t *testing.T) {
 	assert := assert.New(t)
 	require := require.New(t)
@@ -556,6 +592,7 @@ func newDefaultConfig() *Config {
 	config, _ = NewConfig([]string{
 		"--providers.google.client-id=id",
 		"--providers.google.client-secret=secret",
+		"--trusted-ip-address=127.0.0.2",
 	})
 
 	// Setup the google providers without running all the config validation
@@ -576,5 +613,6 @@ func newHTTPRequest(method, target string) *http.Request {
 	r.Header.Add("X-Forwarded-Proto", u.Scheme)
 	r.Header.Add("X-Forwarded-Host", u.Host)
 	r.Header.Add("X-Forwarded-Uri", u.RequestURI())
+	r.Header.Add("X-Forwarded-For", "127.0.0.1")
 	return r
 }