[feature] Enforce OAuth token scopes (#3835)

* move tokenauth to apiutil

* enforce scopes

* docs

* update test models, remove deprecated "follow"

* file header

* tests

* tweak scope matcher

* simplify...

* fix tests

* log user out of settings panel in case of oauth error

internal/api/util/auth.go

@@ -0,0 +1,152 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package util
+
+import (
+	"errors"
+	"slices"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+	"github.com/superseriousbusiness/oauth2/v4"
+)
+
+// Auth wraps an authorized token, application, user, and account.
+// It is used in the functions GetAuthed and MustAuth.
+// Because the user might *not* be authed, any of the fields in this struct
+// might be nil, so make sure to check that when you're using this struct anywhere.
+type Auth struct {
+	Token       oauth2.TokenInfo
+	Application *gtsmodel.Application
+	User        *gtsmodel.User
+	Account     *gtsmodel.Account
+}
+
+// TokenAuth is a convenience function for returning an TokenAuth struct from a gin context.
+// In essence, it tries to extract a token, application, user, and account from the context,
+// and then sets them on a struct for convenience.
+//
+// If any are not present in the context, they will be set to nil on the returned TokenAuth struct.
+//
+// If *ALL* are not present, then nil and an error will be returned.
+//
+// If something goes wrong during parsing, then nil and an error will be returned (consider this not authed).
+// TokenAuth is like GetAuthed, but will fail if one of the requirements is not met.
+func TokenAuth(
+	c *gin.Context,
+	requireToken bool,
+	requireApp bool,
+	requireUser bool,
+	requireAccount bool,
+	requireScope ...Scope,
+) (*Auth, gtserror.WithCode) {
+	var (
+		ctx = c.Copy()
+		a   = &Auth{}
+		i   interface{}
+		ok  bool
+	)
+
+	i, ok = ctx.Get(oauth.SessionAuthorizedToken)
+	if ok {
+		parsed, ok := i.(oauth2.TokenInfo)
+		if !ok {
+			const errText = "could not parse token from session context"
+			return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+		}
+		a.Token = parsed
+	}
+
+	i, ok = ctx.Get(oauth.SessionAuthorizedApplication)
+	if ok {
+		parsed, ok := i.(*gtsmodel.Application)
+		if !ok {
+			const errText = "could not parse application from session context"
+			return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+		}
+		a.Application = parsed
+	}
+
+	i, ok = ctx.Get(oauth.SessionAuthorizedUser)
+	if ok {
+		parsed, ok := i.(*gtsmodel.User)
+		if !ok {
+			const errText = "could not parse user from session context"
+			return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+		}
+		a.User = parsed
+	}
+
+	i, ok = ctx.Get(oauth.SessionAuthorizedAccount)
+	if ok {
+		parsed, ok := i.(*gtsmodel.Account)
+		if !ok {
+			const errText = "could not parse account from session context"
+			return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+		}
+		a.Account = parsed
+	}
+
+	if requireToken && a.Token == nil {
+		const errText = "token not supplied"
+		return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+	}
+
+	if requireApp && a.Application == nil {
+		const errText = "application not supplied"
+		return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+	}
+
+	if requireUser && a.User == nil {
+		const errText = "user not supplied or not authorized"
+		return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+	}
+
+	if requireAccount && a.Account == nil {
+		const errText = "account not supplied or not authorized"
+		return nil, gtserror.NewErrorUnauthorized(errors.New(errText), errText)
+	}
+
+	if len(requireScope) != 0 {
+		// We need to match one of the
+		// required scopes, check if we can.
+		hasScopes := strings.Split(a.Token.GetScope(), " ")
+		scopeOK := slices.ContainsFunc(
+			hasScopes,
+			func(hasScope string) bool {
+				for _, requiredScope := range requireScope {
+					if Scope(hasScope).Permits(requiredScope) {
+						// Got it.
+						return true
+					}
+				}
+				return false
+			},
+		)
+
+		if !scopeOK {
+			const errText = "token has insufficient scope permission"
+			return nil, gtserror.NewErrorForbidden(errors.New(errText), errText)
+		}
+	}
+
+	return a, nil
+}