1/*
2Copyright 2015 The Perkeep Authors
3
4Licensed under the Apache License, Version 2.0 (the "License");
5you may not use this file except in compliance with the License.
6You may obtain a copy of the License at
7
8     http://www.apache.org/licenses/LICENSE-2.0
9
10Unless required by applicable law or agreed to in writing, software
11distributed under the License is distributed on an "AS IS" BASIS,
12WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13See the License for the specific language governing permissions and
14limitations under the License.
15*/
16
17// Package oauthutil contains OAuth 2 related utilities.
18package oauthutil // import "go4.org/oauthutil"
19
20import (
21	"encoding/json"
22	"errors"
23	"fmt"
24	"time"
25
26	"go4.org/wkfs"
27	"golang.org/x/oauth2"
28)
29
30// TitleBarRedirectURL is the OAuth2 redirect URL to use when the authorization
31// code should be returned in the title bar of the browser, with the page text
32// prompting the user to copy the code and paste it in the application.
33const TitleBarRedirectURL = "urn:ietf:wg:oauth:2.0:oob"
34
35// ErrNoAuthCode is returned when Token() has not found any valid cached token
36// and TokenSource does not have an AuthCode for getting a new token.
37var ErrNoAuthCode = errors.New("oauthutil: unspecified TokenSource.AuthCode")
38
39// TokenSource is an implementation of oauth2.TokenSource. It uses CacheFile to store and
40// reuse the the acquired token, and AuthCode to provide the authorization code that will be
41// exchanged for a token otherwise.
42type TokenSource struct {
43	Config *oauth2.Config
44
45	// CacheFile is where the token will be stored JSON-encoded. Any call to Token
46	// first tries to read a valid token from CacheFile.
47	CacheFile string
48
49	// AuthCode provides the authorization code that Token will exchange for a token.
50	// It usually is a way to prompt the user for the code. If CacheFile does not provide
51	// a token and AuthCode is nil, Token returns ErrNoAuthCode.
52	AuthCode func() string
53}
54
55var errExpiredToken = errors.New("expired token")
56
57// cachedToken returns the token saved in cacheFile. It specifically returns
58// errTokenExpired if the token is expired.
59func cachedToken(cacheFile string) (*oauth2.Token, error) {
60	tok := new(oauth2.Token)
61	tokenData, err := wkfs.ReadFile(cacheFile)
62	if err != nil {
63		return nil, err
64	}
65	if err = json.Unmarshal(tokenData, tok); err != nil {
66		return nil, err
67	}
68	if !tok.Valid() {
69		if tok != nil && time.Now().After(tok.Expiry) {
70			return nil, errExpiredToken
71		}
72		return nil, errors.New("invalid token")
73	}
74	return tok, nil
75}
76
77// Token first tries to find a valid token in CacheFile, and otherwise uses
78// Config and AuthCode to fetch a new token. This new token is saved in CacheFile
79// (if not blank). If CacheFile did not provide a token and AuthCode is nil,
80// ErrNoAuthCode is returned.
81func (src TokenSource) Token() (*oauth2.Token, error) {
82	var tok *oauth2.Token
83	var err error
84	if src.CacheFile != "" {
85		tok, err = cachedToken(src.CacheFile)
86		if err == nil {
87			return tok, nil
88		}
89		if err != errExpiredToken {
90			fmt.Printf("Error getting token from %s: %v\n", src.CacheFile, err)
91		}
92	}
93	if src.AuthCode == nil {
94		return nil, ErrNoAuthCode
95	}
96	tok, err = src.Config.Exchange(oauth2.NoContext, src.AuthCode())
97	if err != nil {
98		return nil, fmt.Errorf("could not exchange auth code for a token: %v", err)
99	}
100	if src.CacheFile == "" {
101		return tok, nil
102	}
103	tokenData, err := json.Marshal(&tok)
104	if err != nil {
105		return nil, fmt.Errorf("could not encode token as json: %v", err)
106	}
107	if err := wkfs.WriteFile(src.CacheFile, tokenData, 0600); err != nil {
108		return nil, fmt.Errorf("could not cache token in %v: %v", src.CacheFile, err)
109	}
110	return tok, nil
111}
112
113// NewRefreshTokenSource returns a token source that obtains its initial token
114// based on the provided config and the refresh token.
115func NewRefreshTokenSource(config *oauth2.Config, refreshToken string) oauth2.TokenSource {
116	var noInitialToken *oauth2.Token = nil
117	return oauth2.ReuseTokenSource(noInitialToken, config.TokenSource(
118		oauth2.NoContext, // TODO: maybe accept a context later.
119		&oauth2.Token{RefreshToken: refreshToken},
120	))
121}
122