lastfm: authentication

cmd/auth.go

@@ -43,10 +43,6 @@ var authCmd = &cobra.Command{
 		redirectURL, err := backends.BuildRedirectURL(viper.GetViper(), backend.Name())
 		cobra.CheckErr(err)
 
-		// Start an HTTP server to listen for the response
-		responseChan := make(chan auth.CodeResponse)
-		auth.RunOauth2CallbackServer(*redirectURL, responseChan)
-
 		// The backend must provide an authentication strategy
 		strategy := backend.OAuth2Strategy(redirectURL)
 
@@ -56,14 +52,20 @@ var authCmd = &cobra.Command{
 
 		state := "somestate" // FIXME: Should be a random string
 		// Redirect user to consent page to ask for permission specified scopes.
-		url := strategy.AuthCodeURL(verifier, state)
-		fmt.Printf("Visit the URL for the auth dialog: %v\n", url)
-		err = browser.OpenURL(url)
+		authUrl := strategy.AuthCodeURL(verifier, state)
+
+		// Start an HTTP server to listen for the response
+		responseChan := make(chan auth.CodeResponse)
+		auth.RunOauth2CallbackServer(*redirectURL, authUrl.Param, responseChan)
+
+		// Open the URL
+		fmt.Printf("Visit the URL for the auth dialog: %v\n", authUrl.Url)
+		err = browser.OpenURL(authUrl.Url)
 		cobra.CheckErr(err)
 
 		// Retrieve the code from the authentication callback
 		code := <-responseChan
-		if code.State != state {
+		if code.State != authUrl.State {
 			cobra.CompErrorln("Error: oauth state mismatch")
 			os.Exit(1)
 		}

go.mod

@@ -44,6 +44,7 @@ require (
 	github.com/rivo/uniseg v0.4.4 // indirect
 	github.com/sagikazarmark/locafero v0.3.0 // indirect
 	github.com/sagikazarmark/slog-shim v0.1.0 // indirect
+	github.com/shkh/lastfm-go v0.0.0-20191215035245-89a801c244e0 // indirect
 	github.com/sourcegraph/conc v0.3.0 // indirect
 	github.com/spf13/afero v1.10.0 // indirect
 	github.com/spf13/cast v1.5.1 // indirect

go.sum

@@ -222,6 +222,8 @@ github.com/sagikazarmark/locafero v0.3.0 h1:zT7VEGWC2DTflmccN/5T1etyKvxSxpHsjb9c
 github.com/sagikazarmark/locafero v0.3.0/go.mod h1:w+v7UsPNFwzF1cHuOajOOzoq4U7v/ig1mpRjqV+Bu1U=
 github.com/sagikazarmark/slog-shim v0.1.0 h1:diDBnUNK9N/354PgrxMywXnAwEr1QZcOr6gto+ugjYE=
 github.com/sagikazarmark/slog-shim v0.1.0/go.mod h1:SrcSrq8aKtyuqEI1uvTDTK1arOWRIczQRv+GVI1AkeQ=
+github.com/shkh/lastfm-go v0.0.0-20191215035245-89a801c244e0 h1:cgqwZtnR+IQfUYDLJ3Kiy4aE+O/wExTzEIg8xwC4Qfs=
+github.com/shkh/lastfm-go v0.0.0-20191215035245-89a801c244e0/go.mod h1:n3nudMl178cEvD44PaopxH9jhJaQzthSxUzLO5iKMy4=
 github.com/sourcegraph/conc v0.3.0 h1:OQTbbt6P72L20UqAkXXuLOj79LfEanQ+YQFNpLA9ySo=
 github.com/sourcegraph/conc v0.3.0/go.mod h1:Sdozi7LEKbFPqYX2/J+iBAM6HpqSLTASQIKqDmF7Mt0=
 github.com/spf13/afero v1.10.0 h1:EaGW2JJh15aKOejeuJ+wpFSHnbd7GE6Wvp3TsNhb6LY=

internal/auth/callback.go

@@ -21,9 +21,9 @@ import (
 	"net/url"
 )
 
-func RunOauth2CallbackServer(redirectURL url.URL, responseChan chan CodeResponse) {
+func RunOauth2CallbackServer(redirectURL url.URL, param string, responseChan chan CodeResponse) {
 	http.HandleFunc(redirectURL.Path, func(w http.ResponseWriter, r *http.Request) {
-		code := r.URL.Query().Get("code")
+		code := r.URL.Query().Get(param)
 		state := r.URL.Query().Get("state")
 		fmt.Fprint(w, "Token received, you can close this window now.")
 		responseChan <- CodeResponse{

internal/auth/strategy.go

@@ -24,11 +24,21 @@ import (
 type OAuth2Strategy interface {
 	Config() oauth2.Config
 
-	AuthCodeURL(verifier string, state string) string
+	AuthCodeURL(verifier string, state string) AuthUrl
 
 	ExchangeToken(code CodeResponse, verifier string) (*oauth2.Token, error)
 }
 
+type AuthUrl struct {
+	// The URL the user must visit to approve access
+	Url string
+	// Random state string passed on to the callback.
+	// Leave empty if the service does not support state.
+	State string
+	// Parameter name of the code passed on to the callback (usually "code")
+	Param string
+}
+
 type CodeResponse struct {
 	Code  string
 	State string
@@ -46,8 +56,13 @@ func (s StandardStrategy) Config() oauth2.Config {
 	return s.conf
 }
 
-func (s StandardStrategy) AuthCodeURL(verifier string, state string) string {
-	return s.conf.AuthCodeURL(state, oauth2.AccessTypeOffline, oauth2.S256ChallengeOption(verifier))
+func (s StandardStrategy) AuthCodeURL(verifier string, state string) AuthUrl {
+	url := s.conf.AuthCodeURL(state, oauth2.AccessTypeOffline, oauth2.S256ChallengeOption(verifier))
+	return AuthUrl{
+		Url:   url,
+		State: state,
+		Param: "code",
+	}
 }
 
 func (s StandardStrategy) ExchangeToken(code CodeResponse, verifier string) (*oauth2.Token, error) {

internal/backends/backends.go

@@ -27,6 +27,7 @@ import (
 	"go.uploadedlobster.com/scotty/internal/backends/dump"
 	"go.uploadedlobster.com/scotty/internal/backends/funkwhale"
 	"go.uploadedlobster.com/scotty/internal/backends/jspf"
+	"go.uploadedlobster.com/scotty/internal/backends/lastfm"
 	"go.uploadedlobster.com/scotty/internal/backends/listenbrainz"
 	"go.uploadedlobster.com/scotty/internal/backends/maloja"
 	"go.uploadedlobster.com/scotty/internal/backends/scrobblerlog"
@@ -80,6 +81,7 @@ var knownBackends = map[string]func() models.Backend{
 	"dump":          func() models.Backend { return &dump.DumpBackend{} },
 	"funkwhale":     func() models.Backend { return &funkwhale.FunkwhaleApiBackend{} },
 	"jspf":          func() models.Backend { return &jspf.JSPFBackend{} },
+	"lastfm":        func() models.Backend { return &lastfm.LastfmApiBackend{} },
 	"listenbrainz":  func() models.Backend { return &listenbrainz.ListenBrainzApiBackend{} },
 	"maloja":        func() models.Backend { return &maloja.MalojaApiBackend{} },
 	"scrobbler-log": func() models.Backend { return &scrobblerlog.ScrobblerLogBackend{} },

internal/backends/deezer/auth.go

@@ -33,8 +33,13 @@ func (s deezerStrategy) Config() oauth2.Config {
 	return s.conf
 }
 
-func (s deezerStrategy) AuthCodeURL(verifier string, state string) string {
-	return s.conf.AuthCodeURL(state, oauth2.AccessTypeOffline, oauth2.S256ChallengeOption(verifier))
+func (s deezerStrategy) AuthCodeURL(verifier string, state string) auth.AuthUrl {
+	url := s.conf.AuthCodeURL(state, oauth2.AccessTypeOffline, oauth2.S256ChallengeOption(verifier))
+	return auth.AuthUrl{
+		Url:   url,
+		State: state,
+		Param: "code",
+	}
 }
 
 func (s deezerStrategy) ExchangeToken(code auth.CodeResponse, verifier string) (*oauth2.Token, error) {

internal/backends/lastfm/auth.go

@@ -0,0 +1,51 @@
+/*
+Copyright © 2023 Philipp Wolfer <phw@uploadedlobster.com>
+
+Scotty is free software: you can redistribute it and/or modify it under the
+terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later version.
+
+Scotty is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+Scotty. If not, see <https://www.gnu.org/licenses/>.
+*/
+
+package lastfm
+
+import (
+	"net/url"
+
+	"github.com/shkh/lastfm-go/lastfm"
+	"go.uploadedlobster.com/scotty/internal/auth"
+	"golang.org/x/oauth2"
+)
+
+type lastfmStrategy struct {
+	client      *lastfm.Api
+	redirectUrl *url.URL
+}
+
+func (s lastfmStrategy) Config() oauth2.Config {
+	return oauth2.Config{}
+}
+
+func (s lastfmStrategy) AuthCodeURL(verifier string, state string) auth.AuthUrl {
+	// Last.fm does not use OAuth2, but the provided authorization flow with
+	// callback URL is close enough we can shoehorn it into the existing
+	// authentication strategy.
+	// TODO: Investigate and use callback-less flow with api.GetAuthTokenUrl(token)
+	url := s.client.GetAuthRequestUrl(s.redirectUrl.String())
+	return auth.AuthUrl{
+		Url:   url,
+		State: "", // last.fm does not use state
+		Param: "token",
+	}
+}
+
+func (s lastfmStrategy) ExchangeToken(code auth.CodeResponse, verifier string) (*oauth2.Token, error) {
+	// The token is directly valid
+	return &oauth2.Token{AccessToken: code.Code}, nil
+}

internal/backends/lastfm/lastfm.go

@@ -0,0 +1,54 @@
+/*
+Copyright © 2023 Philipp Wolfer <phw@uploadedlobster.com>
+
+Scotty is free software: you can redistribute it and/or modify it under the
+terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later version.
+
+Scotty is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+Scotty. If not, see <https://www.gnu.org/licenses/>.
+*/
+
+package lastfm
+
+import (
+	"net/url"
+
+	"github.com/shkh/lastfm-go/lastfm"
+	"github.com/spf13/viper"
+	"go.uploadedlobster.com/scotty/internal/auth"
+	"go.uploadedlobster.com/scotty/internal/models"
+	"golang.org/x/oauth2"
+)
+
+type LastfmApiBackend struct {
+	client *lastfm.Api
+}
+
+func (b *LastfmApiBackend) Name() string { return "lastfm" }
+
+func (b *LastfmApiBackend) FromConfig(config *viper.Viper) models.Backend {
+	clientId := config.GetString("client-id")
+	clientSecret := config.GetString("client-secret")
+	b.client = lastfm.New(clientId, clientSecret)
+	return b
+}
+
+func (b *LastfmApiBackend) OAuth2Strategy(redirectUrl *url.URL) auth.OAuth2Strategy {
+	return lastfmStrategy{
+		client:      b.client,
+		redirectUrl: redirectUrl,
+	}
+}
+
+func (b *LastfmApiBackend) OAuth2Setup(token oauth2.TokenSource) error {
+	t, err := token.Token()
+	if err != nil {
+		return err
+	}
+	return b.client.LoginWithToken(t.AccessToken)
+}

scotty.example.toml

@@ -86,6 +86,17 @@ backend       = "deezer"
 client-id     = ""
 client-secret = ""
 
+[service.lastfm]
+backend       = "lastfm"
+# Your Last.fm username
+username      = ""
+# You need to register an application on https://www.last.fm/api/account/create
+# and set the API ID and shared secret below.
+# When registering use "http://127.0.0.1:2222/callback/lastfm" as the
+# callback URI.
+client-id     = ""
+client-secret = ""
+
 [service.dump]
 # This backend allows writing listens and loves as console output. Useful for
 # debugging the export from other services.