feat(oidc): add pkce support (authelia#2924)

Implements Proof Key for Code Exchange for OpenID Connect Authorization Code Flow. By default this is enabled for the public client type and requires the S256 challenge method.

Closes authelia#2921

config.template.yml

@@ -684,6 +684,10 @@ notifier:
     ## security reasons.
     # minimum_parameter_entropy: 8
 
+    ## SECURITY NOTICE: It's not recommended changing this option, and highly discouraged to have it set to 'never'
+    ## for security reasons.
+    # enforce_pkce: public_clients_only
+
     ## Clients is a list of known clients and their configuration.
     # clients:
       # -

docs/configuration/identity-providers/oidc.md

@@ -34,6 +34,7 @@ identity_providers:
     id_token_lifespan: 1h
     refresh_token_lifespan: 90m
     enable_client_debug_messages: false
+    enforce_pkce: public_clients_only
     clients:
       - id: myapp
         description: My Application
@@ -184,6 +185,39 @@ This controls the minimum length of the `nonce` and `state` parameters.
 make certain scenarios less secure. It is highly encouraged that if your OpenID Connect RP does not send these parameters
 or sends parameters with a lower length than the default that they implement a change rather than changing this value.
 
+### enforce_pkce
+<div markdown="1">
+type: string
+{: .label .label-config .label-purple } 
+default: public_clients_only
+{: .label .label-config .label-blue }
+required: no
+{: .label .label-config .label-green }
+</div>
+
+[Proof Key for Code Exchange](https://datatracker.ietf.org/doc/html/rfc7636) enforcement policy: if specified, must be either `never`, `public_clients_only` or `always`.
+
+If set to `public_clients_only` (default), PKCE will be required for public clients using the Authorization Code flow.
+
+When set to `always`, PKCE will be required for all clients using the Authorization Code flow.
+
+***Security Notice:*** Changing this value to `never` is generally discouraged, reducing it from the default can theoretically
+make certain client-side applications (mobile applications, SPA) vulnerable to CSRF and authorization code interception attacks.
+
+### enable_pkce_plain_challenge
+<div markdown="1">
+type: boolean
+{: .label .label-config .label-purple }
+default: false
+{: .label .label-config .label-blue }
+required: no
+{: .label .label-config .label-green }
+</div>
+
+Allows PKCE `plain` challenges when set to `true`.
+
+***Security Notice:*** Changing this value is generally discouraged. Applications should use the `S256` PKCE challenge method instead.
+
 ### clients
 
 A list of clients to configure. The options for each client are described below.

internal/configuration/config.template.yml

@@ -684,6 +684,10 @@ notifier:
     ## security reasons.
     # minimum_parameter_entropy: 8
 
+    ## SECURITY NOTICE: It's not recommended changing this option, and highly discouraged to have it set to 'never'
+    ## for security reasons.
+    # enforce_pkce: public_clients_only
+
     ## Clients is a list of known clients and their configuration.
     # clients:
       # -

internal/configuration/schema/identity_providers.go

@@ -21,6 +21,9 @@ type OpenIDConnectConfiguration struct {
 	EnableClientDebugMessages bool `koanf:"enable_client_debug_messages"`
 	MinimumParameterEntropy   int  `koanf:"minimum_parameter_entropy"`
 
+	EnforcePKCE              string `koanf:"enforce_pkce"`
+	EnablePKCEPlainChallenge bool   `koanf:"enable_pkce_plain_challenge"`
+
 	Clients []OpenIDConnectClientConfiguration `koanf:"clients"`
 }
 
@@ -49,6 +52,7 @@ var DefaultOpenIDConnectConfiguration = OpenIDConnectConfiguration{
 	AuthorizeCodeLifespan: time.Minute,
 	IDTokenLifespan:       time.Hour,
 	RefreshTokenLifespan:  time.Minute * 90,
+	EnforcePKCE:           "public_clients_only",
 }
 
 // DefaultOpenIDConnectClientConfiguration contains defaults for OIDC Clients.

internal/configuration/validator/const.go

@@ -121,6 +121,9 @@ const (
 		"more clients configured"
 	errFmtOIDCNoPrivateKey = "identity_providers: oidc: option 'issuer_private_key' is required"
 
+	errFmtOIDCEnforcePKCEInvalidValue = "identity_providers: oidc: option 'enforce_pkce' must be 'never', " +
+		"'public_clients_only' or 'always', but it is configured as '%s'"
+
 	errFmtOIDCClientsDuplicateID = "identity_providers: oidc: one or more clients have the same id but all client" +
 		"id's must be unique"
 	errFmtOIDCClientsWithEmptyID = "identity_providers: oidc: one or more clients have been configured with " +

internal/configuration/validator/identity_providers.go

@@ -41,6 +41,14 @@ func validateOIDC(config *schema.OpenIDConnectConfiguration, validator *schema.S
 			validator.PushWarning(fmt.Errorf(errFmtOIDCServerInsecureParameterEntropy, config.MinimumParameterEntropy))
 		}
 
+		if config.EnforcePKCE == "" {
+			config.EnforcePKCE = schema.DefaultOpenIDConnectConfiguration.EnforcePKCE
+		}
+
+		if config.EnforcePKCE != "never" && config.EnforcePKCE != "public_clients_only" && config.EnforcePKCE != "always" {
+			validator.Push(fmt.Errorf(errFmtOIDCEnforcePKCEInvalidValue, config.EnforcePKCE))
+		}
+
 		validateOIDCClients(config, validator)
 
 		if len(config.Clients) == 0 {

internal/configuration/validator/identity_providers_test.go

@@ -29,6 +29,24 @@ func TestShouldRaiseErrorWhenInvalidOIDCServerConfiguration(t *testing.T) {
 	assert.EqualError(t, validator.Errors()[1], errFmtOIDCNoClientsConfigured)
 }
 
+func TestShouldRaiseErrorWhenOIDCPKCEEnforceValueInvalid(t *testing.T) {
+	validator := schema.NewStructValidator()
+	config := &schema.IdentityProvidersConfiguration{
+		OIDC: &schema.OpenIDConnectConfiguration{
+			HMACSecret:       "rLABDrx87et5KvRHVUgTm3pezWWd8LMN",
+			IssuerPrivateKey: "key-material",
+			EnforcePKCE:      "invalid",
+		},
+	}
+
+	ValidateIdentityProviders(config, validator)
+
+	require.Len(t, validator.Errors(), 2)
+
+	assert.EqualError(t, validator.Errors()[0], "identity_providers: oidc: option 'enforce_pkce' must be 'never', 'public_clients_only' or 'always', but it is configured as 'invalid'")
+	assert.EqualError(t, validator.Errors()[1], errFmtOIDCNoClientsConfigured)
+}
+
 func TestShouldRaiseErrorWhenOIDCServerIssuerPrivateKeyPathInvalid(t *testing.T) {
 	validator := schema.NewStructValidator()
 	config := &schema.IdentityProvidersConfiguration{

internal/handlers/handler_oidc_wellknown.go

@@ -74,6 +74,7 @@ func oidcWellKnown(ctx *middlewares.AutheliaCtx) {
 			oidc.ClaimPreferredUsername,
 			oidc.ClaimDisplayName,
 		},
+		CodeChallengeMethodsSupported: []string{"S256"},
 
 		RequestURIParameterSupported:       false,
 		BackChannelLogoutSupported:         false,
@@ -82,6 +83,10 @@ func oidcWellKnown(ctx *middlewares.AutheliaCtx) {
 		FrontChannelLogoutSessionSupported: false,
 	}
 
+	if ctx.Configuration.IdentityProviders.OIDC.EnablePKCEPlainChallenge {
+		wellKnown.CodeChallengeMethodsSupported = append(wellKnown.CodeChallengeMethodsSupported, "plain")
+	}
+
 	ctx.SetContentType("application/json")
 
 	if err := json.NewEncoder(ctx).Encode(wellKnown); err != nil {

internal/oidc/provider.go

@@ -23,12 +23,15 @@ func NewOpenIDConnectProvider(configuration *schema.OpenIDConnectConfiguration)
 	provider.Store = NewOpenIDConnectStore(configuration)
 
 	composeConfiguration := &compose.Config{
-		AccessTokenLifespan:        configuration.AccessTokenLifespan,
-		AuthorizeCodeLifespan:      configuration.AuthorizeCodeLifespan,
-		IDTokenLifespan:            configuration.IDTokenLifespan,
-		RefreshTokenLifespan:       configuration.RefreshTokenLifespan,
-		SendDebugMessagesToClients: configuration.EnableClientDebugMessages,
-		MinParameterEntropy:        configuration.MinimumParameterEntropy,
+		AccessTokenLifespan:            configuration.AccessTokenLifespan,
+		AuthorizeCodeLifespan:          configuration.AuthorizeCodeLifespan,
+		IDTokenLifespan:                configuration.IDTokenLifespan,
+		RefreshTokenLifespan:           configuration.RefreshTokenLifespan,
+		SendDebugMessagesToClients:     configuration.EnableClientDebugMessages,
+		MinParameterEntropy:            configuration.MinimumParameterEntropy,
+		EnforcePKCE:                    configuration.EnforcePKCE == "always",
+		EnforcePKCEForPublicClients:    configuration.EnforcePKCE != "never",
+		EnablePKCEPlainChallengeMethod: configuration.EnablePKCEPlainChallenge,
 	}
 
 	keyManager, err := NewKeyManagerWithConfiguration(configuration)
@@ -82,7 +85,7 @@ func NewOpenIDConnectProvider(configuration *schema.OpenIDConnectConfiguration)
 		compose.OAuth2TokenIntrospectionFactory,
 		compose.OAuth2TokenRevocationFactory,
 
-		// compose.OAuth2PKCEFactory,.
+		compose.OAuth2PKCEFactory,
 	)
 
 	provider.herodot = herodot.NewJSONWriter(nil)

internal/oidc/types.go

@@ -86,11 +86,12 @@ type WellKnownConfiguration struct {
 	Algorithms         []string `json:"id_token_signing_alg_values_supported"`
 	UserinfoAlgorithms []string `json:"userinfo_signing_alg_values_supported"`
 
-	SubjectTypesSupported  []string `json:"subject_types_supported"`
-	ResponseTypesSupported []string `json:"response_types_supported"`
-	ResponseModesSupported []string `json:"response_modes_supported"`
-	ScopesSupported        []string `json:"scopes_supported"`
-	ClaimsSupported        []string `json:"claims_supported"`
+	SubjectTypesSupported         []string `json:"subject_types_supported"`
+	ResponseTypesSupported        []string `json:"response_types_supported"`
+	ResponseModesSupported        []string `json:"response_modes_supported"`
+	ScopesSupported               []string `json:"scopes_supported"`
+	ClaimsSupported               []string `json:"claims_supported"`
+	CodeChallengeMethodsSupported []string `json:"code_challenge_methods_supported"`
 
 	RequestURIParameterSupported       bool `json:"request_uri_parameter_supported"`
 	BackChannelLogoutSupported         bool `json:"backchannel_logout_supported"`