[feature] Federate pinned posts (aka featuredCollection) in and out (#1560)

* start fiddling

* the ol' fiddle + update

* start working on fetching statuses

* poopy doopy doo where r u uwu

* further adventures in featuring statuses

* finishing up

* fmt

* simply status unpin loop

* move empty featured check back to caller function

* remove unnecessary log.WithContext calls

* remove unnecessary IsIRI() checks

* add explanatory comment about status URIs

* change log level to error

* better test names

internal/processing/fedi/common.go

@@ -0,0 +1,60 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org
+
+   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 fedi
+
+import (
+	"context"
+	"fmt"
+	"net/url"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/transport"
+)
+
+func (p *Processor) authenticate(ctx context.Context, requestedUsername string) (requestedAccount, requestingAccount *gtsmodel.Account, errWithCode gtserror.WithCode) {
+	requestedAccount, err := p.db.GetAccountByUsernameDomain(ctx, requestedUsername, "")
+	if err != nil {
+		errWithCode = gtserror.NewErrorNotFound(fmt.Errorf("database error getting account with username %s: %s", requestedUsername, err))
+		return
+	}
+
+	var requestingAccountURI *url.URL
+	requestingAccountURI, errWithCode = p.federator.AuthenticateFederatedRequest(ctx, requestedUsername)
+	if errWithCode != nil {
+		return
+	}
+
+	if requestingAccount, err = p.federator.GetAccountByURI(transport.WithFastfail(ctx), requestedUsername, requestingAccountURI, false); err != nil {
+		errWithCode = gtserror.NewErrorUnauthorized(err)
+		return
+	}
+
+	blocked, err := p.db.IsBlocked(ctx, requestedAccount.ID, requestingAccount.ID, true)
+	if err != nil {
+		errWithCode = gtserror.NewErrorInternalError(err)
+		return
+	}
+
+	if blocked {
+		errWithCode = gtserror.NewErrorUnauthorized(fmt.Errorf("block exists between accounts %s and %s", requestedAccount.ID, requestingAccount.ID))
+	}
+
+	return
+}