extractor.go

package request

import (
	"errors"
	"net/http"
	"strings"
)

// Errors
var (
	ErrNoTokenInRequest = errors.New("no token present in request")
)

// Extractor is an interface for extracting a token from an HTTP request.
// The ExtractToken method should return a token string or an error.
// If no token is present, you must return ErrNoTokenInRequest.
type Extractor interface {
	ExtractToken(*http.Request) (string, error)
}

// HeaderExtractor is an extractor for finding a token in a header.
// Looks at each specified header in order until there's a match
type HeaderExtractor []string

func (e HeaderExtractor) ExtractToken(req *http.Request) (string, error) {
	// loop over header names and return the first one that contains data
	for _, header := range e {
		if ah := req.Header.Get(header); ah != "" {
			return ah, nil
		}
	}
	return "", ErrNoTokenInRequest
}

// ArgumentExtractor extracts a token from request arguments.  This includes a POSTed form or
// GET URL arguments.  Argument names are tried in order until there's a match.
// This extractor calls `ParseMultipartForm` on the request
type ArgumentExtractor []string

func (e ArgumentExtractor) ExtractToken(req *http.Request) (string, error) {
	// Make sure form is parsed
	req.ParseMultipartForm(10e6)

	// loop over arg names and return the first one that contains data
	for _, arg := range e {
		if ah := req.Form.Get(arg); ah != "" {
			return ah, nil
		}
	}

	return "", ErrNoTokenInRequest
}

// MultiExtractor tries Extractors in order until one returns a token string or an error occurs
type MultiExtractor []Extractor

func (e MultiExtractor) ExtractToken(req *http.Request) (string, error) {
	// loop over header names and return the first one that contains data
	for _, extractor := range e {
		if tok, err := extractor.ExtractToken(req); tok != "" {
			return tok, nil
		} else if !errors.Is(err, ErrNoTokenInRequest) {
			return "", err
		}
	}
	return "", ErrNoTokenInRequest
}

// PostExtractionFilter wraps an Extractor in this to post-process the value before it's handed off.
// See AuthorizationHeaderExtractor for an example
type PostExtractionFilter struct {
	Extractor
	Filter func(string) (string, error)
}

func (e *PostExtractionFilter) ExtractToken(req *http.Request) (string, error) {
	if tok, err := e.Extractor.ExtractToken(req); tok != "" {
		return e.Filter(tok)
	} else {
		return "", err
	}
}

// BearerExtractor extracts a token from the Authorization header.
// The header is expected to match the format "Bearer XX", where "XX" is the
// JWT token.
type BearerExtractor struct{}

func (e BearerExtractor) ExtractToken(req *http.Request) (string, error) {
	tokenHeader := req.Header.Get("Authorization")
	// The usual convention is for "Bearer" to be title-cased. However, there's no
	// strict rule around this, and it's best to follow the robustness principle here.
	if tokenHeader == "" || !strings.HasPrefix(strings.ToLower(tokenHeader), "bearer ") {
		return "", ErrNoTokenInRequest
	}
	return tokenHeader[7:], nil
}