Support imaps with oauthbearer authentication (Gmail)

    imaps+oauthbearer://user:token@host?token_endpoint=...

 - the config Source password is used as access token if
   no token_endpoint parameter is set
 - the config Source password is used as refresh token if
   token_endpoint parameter is set, and used to exchange
   with an access token

The implementation has only been tested with Gmail.

    source = imaps+oauthbearer://{username}:{refersh_token}@imap.gmail.com:993? \
    client_id=XX&\
    client_secret=XX&\
    token_endpoint=https%3A%2F%2Faccounts.google.com%2Fo%2Foauth2%2Ftoken

client credentials created with

    https://console.developers.google.com/apis/credentials

refresh token created with

    https://github.com/google/gmail-oauth2-tools/blob/master/python/oauth2.py

rel: https://todo.sr.ht/~sircmpwn/aerc2/42

5 files changed, 100 insertions, 8 deletions

diff --git a/doc/aerc-imap.5.scd b/doc/aerc-imap.5.scd
index 12dcfbe..4307238 100644
--- a/doc/aerc-imap.5.scd
+++ b/doc/aerc-imap.5.scd
@@ -19,7 +19,7 @@ In accounts.conf (see *aerc-config*(5)), the following IMAP-specific options are
 available:
 
 *source*
-	imap[s][+insecure]://username[:password]@hostname[:port]
+	imap[s][+insecure|+oauthbearer]://username[:password]@hostname[:port]?[:oauth2_params]
 
 	Remember that all fields must be URL encoded. The "@" symbol, when URL
 	encoded, is *%40*.
@@ -35,6 +35,22 @@ available:
 	*imaps*:
 		IMAP with TLS/SSL
 
+	*imaps+oauthbearer://*
+		IMAP with TLS/SSL using OAUTHBEARER Authentication
+
+		*oauth2_params:*
+
+		If specified, the configured password is used as an refresh token that
+		is exhanged with an access token
+
+		- token_endpoint (required)
+		- client_id (optional)
+		- client_secret (optional)
+		- scope (optional)
+
+		Example:
+		imaps+oauthbearer://...?token_endpoint=https://...&client_id=
+
 *source-cred-cmd*
 	Specifies the command to run to get the password for the IMAP
 	account. This command will be run using `sh -c [command]`. If a
diff --git a/go.mod b/go.mod
index 1c3d156..ab0a033 100644
--- a/go.mod
+++ b/go.mod
@@ -11,7 +11,7 @@ require (
 	github.com/emersion/go-imap v1.0.0-beta.6
 	github.com/emersion/go-imap-idle v0.0.0-20190519112320-2704abd7050e
 	github.com/emersion/go-message v0.10.3
-	github.com/emersion/go-sasl v0.0.0-20190520160400-47d427600317
+	github.com/emersion/go-sasl v0.0.0-20190704090222-36b50694675c
 	github.com/emersion/go-smtp v0.11.1
 	github.com/gdamore/tcell v1.1.2
 	github.com/go-ini/ini v1.42.0
@@ -28,6 +28,7 @@ require (
 	github.com/smartystreets/assertions v1.0.0 // indirect
 	github.com/smartystreets/goconvey v0.0.0-20190330032615-68dc04aab96a // indirect
 	github.com/stretchr/testify v1.3.0
+	golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45
 	golang.org/x/sys v0.0.0-20190602015325-4c4f7f33c9ed // indirect
 	gopkg.in/ini.v1 v1.42.0 // indirect
 )
diff --git a/go.sum b/go.sum
index 6c33d94..ab11314 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,4 @@
+cloud.google.com/go v0.34.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
 git.sr.ht/~sircmpwn/getopt v0.0.0-20190214165041-9a4f886f9fc7 h1:xTFH5S/3ltiRvAtETLLDFWm5nVIouT5GeCPHm8UaVEU=
 git.sr.ht/~sircmpwn/getopt v0.0.0-20190214165041-9a4f886f9fc7/go.mod h1:wMEGFFFNuPos7vHmWXfszqImLppbc0wEhh6JBfJIUgw=
 git.sr.ht/~sircmpwn/getopt v0.0.0-20190609193657-e7e23d1cd3a3 h1:2l17fmuVbiS2cSx1m8e8GbikDUjAT5lril3/+XQsZAs=
@@ -28,6 +29,8 @@ github.com/emersion/go-sasl v0.0.0-20161116183048-7e096a0a6197 h1:rDJPbyliyym8ZL
 github.com/emersion/go-sasl v0.0.0-20161116183048-7e096a0a6197/go.mod h1:G/dpzLu16WtQpBfQ/z3LYiYJn3ZhKSGWn83fyoyQe/k=
 github.com/emersion/go-sasl v0.0.0-20190520160400-47d427600317 h1:tYZxAY8nu3JJQKios9f27Sbvbkfm4XHXT476gVtszu0=
 github.com/emersion/go-sasl v0.0.0-20190520160400-47d427600317/go.mod h1:G/dpzLu16WtQpBfQ/z3LYiYJn3ZhKSGWn83fyoyQe/k=
+github.com/emersion/go-sasl v0.0.0-20190704090222-36b50694675c h1:Spm8jy+jWYG/Dn6ygbq/LBW/6M27kg59GK+FkKjexuw=
+github.com/emersion/go-sasl v0.0.0-20190704090222-36b50694675c/go.mod h1:G/dpzLu16WtQpBfQ/z3LYiYJn3ZhKSGWn83fyoyQe/k=
 github.com/emersion/go-smtp v0.11.1 h1:2IBWhU2zjrfOOmZal3qRxVsfYnf0rN+ccImZrjnMT7E=
 github.com/emersion/go-smtp v0.11.1/go.mod h1:CfUbM5NgspbOMHFEgCdoK2PVrKt48HAPtL8hnahwfYg=
 github.com/emersion/go-textwrapper v0.0.0-20160606182133-d0e65e56babe h1:40SWqY0zE3qCi6ZrtTf5OUdNm5lDnGnjRSq9GgmeTrg=
@@ -36,6 +39,7 @@ github.com/gdamore/encoding v1.0.0 h1:+7OoQ1Bc6eTm5niUzBa0Ctsh6JbMW6Ra+YNuAtDBdk
 github.com/gdamore/encoding v1.0.0/go.mod h1:alR0ol34c49FCSBLjhosxzcPHQbf2trDkoo5dl+VrEg=
 github.com/go-ini/ini v1.42.0 h1:TWr1wGj35+UiWHlBA8er89seFXxzwFn11spilrrj+38=
 github.com/go-ini/ini v1.42.0/go.mod h1:ByCAeIL28uOIIG0E3PJtZPDL8WnHpFKFOtgjp+3Ies8=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf h1:7+FW5aGwISbqUtkfmIpZJGRgNFg2ioYPvFaUxdqpDsg=
 github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf/go.mod h1:RpwtwJQFrIEPstU94h88MWPXP2ektJZ8cZ0YntAmXiE=
 github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1 h1:EGx4pi6eqNxGaHF6qqu48+N2wcFQ5qg5FXgOdqsJ5d8=
@@ -77,7 +81,13 @@ github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/image v0.0.0-20190523035834-f03afa92d3ff/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
+golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190108225652-1e06a53dbb7e/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a h1:oWX7TPOiFAMXLq8o0ikBYfCJVlRHBcsciT5bXOrH628=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45 h1:SVwTIAaPC2U/AvvLNZ2a7OVsmBpC8L5BlwK1whH3hm0=
+golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
+golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190602015325-4c4f7f33c9ed h1:uPxWBzB3+mlnjy9W58qY1j/cjyFjutgw/Vhan2zLy/A=
@@ -88,5 +98,6 @@ golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190328211700-ab21143f2384/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=
 gopkg.in/ini.v1 v1.42.0 h1:7N3gPTt50s8GuLortA00n8AqRTk75qOP98+mTPpgzRk=
 gopkg.in/ini.v1 v1.42.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
diff --git a/lib/oauthbearer.go b/lib/oauthbearer.go
new file mode 100644
index 0000000..5bcba60
--- /dev/null
+++ b/lib/oauthbearer.go
@@ -0,0 +1,42 @@
+package lib
+
+import (
+	"context"
+	"fmt"
+	"github.com/emersion/go-imap/client"
+	"github.com/emersion/go-sasl"
+	"golang.org/x/oauth2"
+)
+
+type OAuthBearer struct {
+	OAuth2  *oauth2.Config
+	Enabled bool
+}
+
+func (c *OAuthBearer) exchangeRefreshToken(refreshToken string) (*oauth2.Token, error) {
+	token := new(oauth2.Token)
+	token.RefreshToken = refreshToken
+	token.TokenType = "Bearer"
+	return c.OAuth2.TokenSource(context.TODO(), token).Token()
+}
+
+func (c *OAuthBearer) Authenticate(username string, password string, client *client.Client) error {
+	if ok, err := client.SupportAuth(sasl.OAuthBearer); err != nil || !ok {
+		return fmt.Errorf("OAuthBearer not supported %v", err)
+	}
+
+	if c.OAuth2.Endpoint.TokenURL != "" {
+		token, err := c.exchangeRefreshToken(password)
+		if err != nil {
+			return err
+		}
+		password = token.AccessToken
+	}
+
+	saslClient := sasl.NewOAuthBearerClient(&sasl.OAuthBearerOptions{
+		Username: username,
+		Token:    password,
+	})
+
+	return client.Authenticate(saslClient)
+}
diff --git a/worker/imap/worker.go b/worker/imap/worker.go
index 88f8b37..de86994 100644
--- a/worker/imap/worker.go
+++ b/worker/imap/worker.go
@@ -9,7 +9,9 @@ import (
 	"github.com/emersion/go-imap"
 	idle "github.com/emersion/go-imap-idle"
 	"github.com/emersion/go-imap/client"
+	"golang.org/x/oauth2"
 
+	"git.sr.ht/~sircmpwn/aerc/lib"
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/worker/types"
 )
@@ -23,11 +25,12 @@ type imapClient struct {
 
 type IMAPWorker struct {
 	config struct {
-		scheme   string
-		insecure bool
-		addr     string
-		user     *url.Userinfo
-		folders  []string
+		scheme      string
+		insecure    bool
+		addr        string
+		user        *url.Userinfo
+		folders     []string
+		oauthBearer lib.OAuthBearer
 	}
 
 	client   *imapClient
@@ -71,6 +74,20 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 			w.config.insecure = true
 		}
 
+		if strings.HasSuffix(w.config.scheme, "+oauthbearer") {
+			w.config.scheme = strings.TrimSuffix(w.config.scheme, "+oauthbearer")
+			w.config.oauthBearer.Enabled = true
+			q := u.Query()
+			if q.Get("token_endpoint") != "" {
+				w.config.oauthBearer.OAuth2 = &oauth2.Config{
+					ClientID:     q.Get("client_id"),
+					ClientSecret: q.Get("client_secret"),
+					Scopes:       []string{q.Get("scope")},
+				}
+				w.config.oauthBearer.OAuth2.Endpoint.TokenURL = q.Get("token_endpoint")
+			}
+		}
+
 		w.config.addr = u.Host
 		if !strings.ContainsRune(w.config.addr, ':') {
 			w.config.addr += ":" + w.config.scheme
@@ -110,7 +127,12 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 			if !hasPassword {
 				// TODO: ask password
 			}
-			if err := c.Login(username, password); err != nil {
+
+			if w.config.oauthBearer.Enabled {
+				if err := w.config.oauthBearer.Authenticate(username, password, c); err != nil {
+					return err
+				}
+			} else if err := c.Login(username, password); err != nil {
 				return err
 			}
 		}