Add OAuth 2.0 backend

auth/oauth2.go

@@ -0,0 +1,87 @@
+package auth
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/rs/zerolog/log"
+
+	"git.sr.ht/~emersion/go-oauth2"
+)
+
+type OAuth2Provider struct {
+	metadata     *oauth2.ServerMetadata
+	clientID     string
+	clientSecret string
+}
+
+// Initializes a new OAuth 2.0 auth provider with the given connection string.
+func NewOAuth2(endpoint, clientID, clientSecret string) (AuthProvider, error) {
+	metadata, err := oauth2.DiscoverServerMetadata(context.Background(), endpoint)
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch OAuth 2.0 server metadata: %v", err)
+	}
+	return &OAuth2Provider{
+		metadata:     metadata,
+		clientID:     clientID,
+		clientSecret: clientSecret,
+	}, nil
+}
+
+func (prov *OAuth2Provider) Middleware() func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			prov.doAuth(next, w, r)
+		})
+	}
+}
+
+func (prov *OAuth2Provider) doAuth(next http.Handler,
+	w http.ResponseWriter, r *http.Request) {
+
+	auth := r.Header.Get("Authorization")
+	authScheme, creds, _ := strings.Cut(auth, " ")
+	var username, accessToken string
+	switch strings.ToLower(authScheme) {
+	case "bearer":
+		accessToken = creds
+	case "basic":
+		username, accessToken, _ = r.BasicAuth()
+	default:
+		w.Header().Add("WWW-Authenticate", `Bearer, Basic realm="Please provide an OAuth access token", charset="UTF-8"`)
+		http.Error(w, "HTTP auth is required", http.StatusUnauthorized)
+		return
+	}
+
+	client := oauth2.Client{
+		Server:       prov.metadata,
+		ClientID:     prov.clientID,
+		ClientSecret: prov.clientSecret,
+	}
+	resp, err := client.Introspect(r.Context(), accessToken)
+	if err != nil || !resp.Active {
+		log.Debug().Err(err).Msg("auth error")
+		http.Error(w, "Invalid access token", http.StatusUnauthorized)
+		return
+	}
+
+	if username != "" && username != resp.Username {
+		http.Error(w, "Invalid username", http.StatusUnauthorized)
+		return
+	}
+
+	if resp.Username == "" {
+		http.Error(w, "OAuth 2.0 server did not send username", http.StatusInternalServerError)
+		return
+	}
+
+	authCtx := AuthContext{
+		AuthMethod: "oauth2",
+		UserName:   resp.Username,
+	}
+	ctx := NewContext(r.Context(), &authCtx)
+	r = r.WithContext(ctx)
+	next.ServeHTTP(w, r)
+}

auth/url.go

@@ -26,6 +26,14 @@ func NewFromURL(authURL string) (AuthProvider, error) {
 		return NewHtpasswd(path)
 	case "null":
 		return NewNull()
+	case "http", "https":
+		if u.User == nil {
+			return nil, fmt.Errorf("missing client ID for OAuth 2.0")
+		}
+		clientID := u.User.Username()
+		clientSecret, _ := u.User.Password()
+		u.User = nil
+		return NewOAuth2(u.String(), clientID, clientSecret)
 	default:
 		return nil, fmt.Errorf("no auth provider found for %s:// URL", u.Scheme)
 	}

doc/tokidoki.8.scd

@@ -74,6 +74,13 @@ URL: *pam://* (no parameters)
 _Note:_ The PAM auth backend must be enabled at build time, as PAM may not be
 available on all platforms.
 
+## OAuth 2.0
+
+The OAuth 2.0 auth backend delegates authentication to the provided OAuth 2.0
+server.
+
+URL: *https://*_client_id_*:*_client_secret_*@*_host_
+
 ## Static file (htpasswd)
 
 The static file auth backend relies on the file format popularized by Apache and

go.mod

@@ -3,6 +3,7 @@ module git.sr.ht/~sircmpwn/tokidoki
 go 1.18
 
 require (
+	git.sr.ht/~emersion/go-oauth2 v0.0.0-20240217160856-2e0d6e20b088
 	github.com/emersion/go-ical v0.0.0-20220601085725-0864dccc089f
 	github.com/emersion/go-imap v1.2.1
 	github.com/emersion/go-sasl v0.0.0-20231106173351-e73c9f7bad43

go.sum

@@ -1,3 +1,5 @@
+git.sr.ht/~emersion/go-oauth2 v0.0.0-20240217160856-2e0d6e20b088 h1:KuPliLD8CQM1WbCHdjHR6mhadIzLaAJCNENmvB1y9gs=
+git.sr.ht/~emersion/go-oauth2 v0.0.0-20240217160856-2e0d6e20b088/go.mod h1:VHj0jSCLIkrfEwmOvJ4+ykpoVbD/YLN7BM523oKKBHc=
 github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/emersion/go-ical v0.0.0-20220601085725-0864dccc089f h1:feGUUxxvOtWVOhTko8Cbmp33a+tU0IMZxMEmnkoAISQ=
 github.com/emersion/go-ical v0.0.0-20220601085725-0864dccc089f/go.mod h1:2MKFUgfNMULRxqZkadG1Vh44we3y5gJAtTBlVsx1BKQ=