Permify / permify

import (

	"context"

	"encoding/json"

	"errors"

	"fmt"

	"io"

	"net/http"

	"strings"

	"github.com/golang-jwt/jwt/v4"

	grpcauth "github.com/grpc-ecosystem/go-grpc-middleware/auth"

	"github.com/hashicorp/go-retryablehttp"

	"github.com/lestrrat-go/jwx/jwk"

	"github.com/Permify/permify/internal/config"

	base "github.com/Permify/permify/pkg/pb/base/v1"

)

// Authenticator - Interface for oidc authenticator

type Authenticator interface {

	Authenticate(ctx context.Context) error

}

type Authn struct {

	// URL of the issuer. This is typically the base URL of the identity provider.

	IssuerURL string

	// Audience for which the token is intended. It must match the audience in the JWT.

	Audience string

	// URL of the JSON Web Key Set (JWKS). This URL hosts public keys used to verify JWT signatures.

	JwksURI string

	// Pointer to an AutoRefresh object from the JWKS library. It helps in automatically refreshing the JWKS at predefined intervals.

	jwksSet *jwk.AutoRefresh

	// List of valid signing methods. Specifies which signing algorithms are considered valid for the JWTs.

	validMethods []string

	// Pointer to a JWT parser object. This is used to parse and validate the JWT tokens.

	jwtParser *jwt.Parser

}

// NewOidcAuthn initializes a new instance of the Authn struct with OpenID Connect (OIDC) configuration.

// It takes in a context for managing cancellation and a configuration object. It returns a pointer to an Authn instance or an error.

func NewOidcAuthn(ctx context.Context, conf config.Oidc) (*Authn, error) {

	// Create a new HTTP client with retry capabilities. This client is used for making HTTP requests, particularly for fetching OIDC configuration.

	client := retryablehttp.NewClient()

	client.Logger = nil // Disable logging for the HTTP client to avoid noisy logs.

	// Fetch the OIDC configuration from the issuer's well-known configuration endpoint.

	oidcConf, err := fetchOIDCConfiguration(client.StandardClient(), strings.TrimSuffix(conf.Issuer, "/")+"/.well-known/openid-configuration")

	if err != nil {

		// If there is an error fetching the OIDC configuration, return nil and the error.

	}

	// Set up automatic refresh of the JSON Web Key Set (JWKS) to ensure the public keys are always up-to-date.

	ar := jwk.NewAutoRefresh(ctx)                                                                                              // Create a new AutoRefresh instance for the JWKS.

	ar.Configure(oidcConf.JWKsURI, jwk.WithHTTPClient(client.StandardClient()), jwk.WithRefreshInterval(conf.RefreshInterval)) // Configure the auto-refresh parameters.

	// Initialize the Authn struct with the OIDC configuration details and other relevant settings.

	oidc := &Authn{

		IssuerURL:    conf.Issuer,                                            // URL of the token issuer.

		Audience:     conf.Audience,                                          // Intended audience of the token.

		JwksURI:      oidcConf.JWKsURI,                                       // URL of the JWKS endpoint.

		validMethods: conf.ValidMethods,                                      // List of acceptable signing methods for the tokens.

		jwtParser:    jwt.NewParser(jwt.WithValidMethods(conf.ValidMethods)), // JWT parser configured with the valid signing methods.

		jwksSet:      ar,                                                     // Set the JWKS auto-refresh instance.

	}

	// Attempt to fetch the JWKS immediately to ensure it's available and valid.

	_, err = oidc.jwksSet.Fetch(ctx, oidc.JwksURI)

	if err != nil {

		// If there is an error fetching the JWKS, return nil and the error.

	}

	// Return the initialized OIDC authentication object and no error.

	return oidc, nil

}

// Authenticate validates the JWT token found in the authorization header of the incoming request.

// It uses the OIDC configuration to validate the token against the issuer's public keys.

func (oidc *Authn) Authenticate(requestContext context.Context) error {

	// Extract the authorization header from the metadata of the incoming gRPC request.

	authHeader, err := grpcauth.AuthFromMD(requestContext, "Bearer")

	if err != nil {

		// If the authorization header is missing or does not start with "Bearer", return an error.

		return errors.New(base.ErrorCode_ERROR_CODE_MISSING_BEARER_TOKEN.String())

	}

	// Parse and validate the JWT token extracted from the authorization header.

	parsedToken, err := oidc.jwtParser.Parse(authHeader, func(token *jwt.Token) (interface{}, error) {

		// Fetch the public keys from the JWKS endpoint configured for the OIDC.

		jwks, err := oidc.jwksSet.Fetch(requestContext, oidc.JwksURI)

		if err != nil {

			// If fetching the JWKS fails, return an error.

		}

		// Retrieve the key ID from the JWT header and find the corresponding key in the JWKS.

		if keyID, ok := token.Header["kid"].(string); ok {

			if key, found := jwks.LookupKeyID(keyID); found {

				// If the key is found, convert it to a usable format.

				var k interface{}

				if err := key.Raw(&k); err != nil {

				}

				return k, nil // Return the public key for JWT signature verification.

			}

			// If the specified key ID is not found in the JWKS, return an error.

			return nil, fmt.Errorf("kid %s not found", keyID)

		}

		// If the JWT does not contain a key ID, return an error.

		return nil, errors.New("kid must be specified in the token header")

	})

	if err != nil {

		// If token parsing or validation fails, return an error indicating the token is invalid.

		return errors.New(base.ErrorCode_ERROR_CODE_INVALID_BEARER_TOKEN.String())

	}

	// Verify the audience of the token matches the expected audience.

	if ok := claims.VerifyAudience(oidc.Audience, true); !ok {

		return errors.New(base.ErrorCode_ERROR_CODE_INVALID_AUDIENCE.String())

	}

	// If all validations pass, return nil indicating the token is valid.

	return nil

}

// Config holds OpenID Connect (OIDC) configuration details.

type Config struct {

	// Issuer is the OIDC provider's unique identifier URL.

	Issuer string `json:"issuer"`

	// JWKsURI is the URL to the JSON Web Key Set (JWKS) provided by the OIDC issuer.

	JWKsURI string `json:"jwks_uri"`

}

// fetchOIDCConfiguration sends an HTTP request to the given URL to fetch the OpenID Connect (OIDC) configuration.

// It requires an HTTP client and the URL from which to fetch the configuration.

func fetchOIDCConfiguration(client *http.Client, url string) (*Config, error) {

	// Send an HTTP GET request to the provided URL to fetch the OIDC configuration.

	// This typically points to the well-known configuration endpoint of the OIDC provider.

	body, err := doHTTPRequest(client, url)

	if err != nil {

		// If there is an error in fetching the configuration (network error, bad response, etc.), return nil and the error.

		return nil, err

	}

	// Parse the JSON response body into an OIDC Config struct.

	// This involves unmarshalling the JSON into a struct that matches the expected fields of the OIDC configuration.

	oidcConfig, err := parseOIDCConfiguration(body)

	if err != nil {

		// If there is an error in parsing the JSON response (missing fields, incorrect format, etc.), return nil and the error.

		return nil, err

	}

	// Return the parsed OIDC configuration and nil as the error (indicating success).

	return oidcConfig, nil

}

// doHTTPRequest makes an HTTP GET request to the specified URL and returns the response body.

func doHTTPRequest(client *http.Client, url string) ([]byte, error) {

	// Create a new HTTP GET request.

	req, err := http.NewRequest("GET", url, nil)

	if err != nil {

		return nil, fmt.Errorf("failed to create HTTP request for OIDC configuration: %s", err)

	}

	// Send the request using the configured HTTP client.

	res, err := client.Do(req)

	if err != nil {

		return nil, fmt.Errorf("failed to execute HTTP request for OIDC configuration: %s", err)

	}

	// Ensure the response body is closed after reading.

	defer res.Body.Close()

	// Check if the HTTP status code indicates success.

	if res.StatusCode != http.StatusOK {

		return nil, fmt.Errorf("received unexpected status code (%d) while fetching OIDC configuration", res.StatusCode)

	}

	// Read the response body.

	body, err := io.ReadAll(res.Body)

	if err != nil {

		// Return an error if reading the response body fails.

		return nil, fmt.Errorf("failed to read response body from OIDC configuration request: %s", err)

	}

	// Return the response body.

	return body, nil

}

// parseOIDCConfiguration decodes the OIDC configuration from the given JSON body.

func parseOIDCConfiguration(body []byte) (*Config, error) {

	var oidcConfig Config

	// Attempt to unmarshal the JSON body into the oidcConfig struct.

	if err := json.Unmarshal(body, &oidcConfig); err != nil {

		return nil, fmt.Errorf("failed to decode OIDC configuration: %s", err)

	}

	if oidcConfig.Issuer == "" {

		return nil, errors.New("issuer value is required but missing in OIDC configuration")

	}

	if oidcConfig.JWKsURI == "" {

		return nil, errors.New("JWKsURI value is required but missing in OIDC configuration")

	}

	// Return the successfully parsed configuration.

	return &oidcConfig, nil

}