echo/middleware/key_auth.go

// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: © 2015 LabStack LLC and Echo contributors

package middleware

import (
	"errors"
	"github.com/labstack/echo/v4"
	"net/http"
)

// KeyAuthConfig defines the config for KeyAuth middleware.
type KeyAuthConfig struct {
	// Skipper defines a function to skip middleware.
	Skipper Skipper

	// KeyLookup is a string in the form of "<source>:<name>" or "<source>:<name>,<source>:<name>" that is used
	// to extract key from the request.
	// Optional. Default value "header:Authorization".
	// Possible values:
	// - "header:<name>" or "header:<name>:<cut-prefix>"
	// 			`<cut-prefix>` is argument value to cut/trim prefix of the extracted value. This is useful if header
	//			value has static prefix like `Authorization: <auth-scheme> <authorisation-parameters>` where part that we
	//			want to cut is `<auth-scheme> ` note the space at the end.
	//			In case of basic authentication `Authorization: Basic <credentials>` prefix we want to remove is `Basic `.
	// - "query:<name>"
	// - "form:<name>"
	// - "cookie:<name>"
	// Multiple sources example:
	// - "header:Authorization,header:X-Api-Key"
	KeyLookup string

	// AuthScheme to be used in the Authorization header.
	// Optional. Default value "Bearer".
	AuthScheme string

	// Validator is a function to validate key.
	// Required.
	Validator KeyAuthValidator

	// ErrorHandler defines a function which is executed for an invalid key.
	// It may be used to define a custom error.
	ErrorHandler KeyAuthErrorHandler

	// ContinueOnIgnoredError allows the next middleware/handler to be called when ErrorHandler decides to
	// ignore the error (by returning `nil`).
	// This is useful when parts of your site/api allow public access and some authorized routes provide extra functionality.
	// In that case you can use ErrorHandler to set a default public key auth value in the request context
	// and continue. Some logic down the remaining execution chain needs to check that (public) key auth value then.
	ContinueOnIgnoredError bool
}

// KeyAuthValidator defines a function to validate KeyAuth credentials.
type KeyAuthValidator func(auth string, c echo.Context) (bool, error)

// KeyAuthErrorHandler defines a function which is executed for an invalid key.
type KeyAuthErrorHandler func(err error, c echo.Context) error

// ErrKeyAuthMissing is error type when KeyAuth middleware is unable to extract value from lookups
type ErrKeyAuthMissing struct {
	Err error
}

// DefaultKeyAuthConfig is the default KeyAuth middleware config.
var DefaultKeyAuthConfig = KeyAuthConfig{
	Skipper:    DefaultSkipper,
	KeyLookup:  "header:" + echo.HeaderAuthorization,
	AuthScheme: "Bearer",
}

// Error returns errors text
func (e *ErrKeyAuthMissing) Error() string {
	return e.Err.Error()
}

// Unwrap unwraps error
func (e *ErrKeyAuthMissing) Unwrap() error {
	return e.Err
}

// KeyAuth returns an KeyAuth middleware.
//
// For valid key it calls the next handler.
// For invalid key, it sends "401 - Unauthorized" response.
// For missing key, it sends "400 - Bad Request" response.
func KeyAuth(fn KeyAuthValidator) echo.MiddlewareFunc {
	c := DefaultKeyAuthConfig
	c.Validator = fn
	return KeyAuthWithConfig(c)
}

// KeyAuthWithConfig returns an KeyAuth middleware with config.
// See `KeyAuth()`.
func KeyAuthWithConfig(config KeyAuthConfig) echo.MiddlewareFunc {
	// Defaults
	if config.Skipper == nil {
		config.Skipper = DefaultKeyAuthConfig.Skipper
	}
	// Defaults
	if config.AuthScheme == "" {
		config.AuthScheme = DefaultKeyAuthConfig.AuthScheme
	}
	if config.KeyLookup == "" {
		config.KeyLookup = DefaultKeyAuthConfig.KeyLookup
	}
	if config.Validator == nil {
		panic("echo: key-auth middleware requires a validator function")
	}

	extractors, cErr := createExtractors(config.KeyLookup, config.AuthScheme)
	if cErr != nil {
		panic(cErr)
	}

	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			if config.Skipper(c) {
				return next(c)
			}

			var lastExtractorErr error
			var lastValidatorErr error
			for _, extractor := range extractors {
				keys, err := extractor(c)
				if err != nil {
					lastExtractorErr = err
					continue
				}
				for _, key := range keys {
					valid, err := config.Validator(key, c)
					if err != nil {
						lastValidatorErr = err
						continue
					}
					if valid {
						return next(c)
					}
					lastValidatorErr = errors.New("invalid key")
				}
			}

			// we are here only when we did not successfully extract and validate any of keys
			err := lastValidatorErr
			if err == nil { // prioritize validator errors over extracting errors
				// ugly part to preserve backwards compatible errors. someone could rely on them
				if lastExtractorErr == errQueryExtractorValueMissing {
					err = errors.New("missing key in the query string")
				} else if lastExtractorErr == errCookieExtractorValueMissing {
					err = errors.New("missing key in cookies")
				} else if lastExtractorErr == errFormExtractorValueMissing {
					err = errors.New("missing key in the form")
				} else if lastExtractorErr == errHeaderExtractorValueMissing {
					err = errors.New("missing key in request header")
				} else if lastExtractorErr == errHeaderExtractorValueInvalid {
					err = errors.New("invalid key in the request header")
				} else {
					err = lastExtractorErr
				}
				err = &ErrKeyAuthMissing{Err: err}
			}

			if config.ErrorHandler != nil {
				tmpErr := config.ErrorHandler(err, c)
				if config.ContinueOnIgnoredError && tmpErr == nil {
					return next(c)
				}
				return tmpErr
			}
			if lastValidatorErr != nil { // prioritize validator errors over extracting errors
				return &echo.HTTPError{
					Code:     http.StatusUnauthorized,
					Message:  "Unauthorized",
					Internal: lastValidatorErr,
				}
			}
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}
	}
}