feat(federation): validate like activities (#3494)

First step on the way to #1680

The PR will

* accept like request on the api
* validate activity in a first level

You can find

* architecture at: https://codeberg.org/meissa/forgejo/src/branch/forgejo-federated-star/docs/unsure-where-to-put/federation-architecture.md

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/3494
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
Co-committed-by: Michael Jerger <michael.jerger@meissa-gmbh.de>

services/context/repository.go

@@ -0,0 +1,25 @@
+// Copyright 2023, 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"net/http"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+)
+
+// RepositoryIDAssignmentAPI returns a middleware to handle context-repo assignment for api routes
+func RepositoryIDAssignmentAPI() func(ctx *APIContext) {
+	return func(ctx *APIContext) {
+		repositoryID := ctx.ParamsInt64(":repository-id")
+
+		var err error
+		repository := new(Repository)
+		repository.Repository, err = repo_model.GetRepositoryByID(ctx, repositoryID)
+		if err != nil {
+			ctx.Error(http.StatusNotFound, "GetRepositoryByID", err)
+		}
+		ctx.Repo = repository
+	}
+}

services/federation/federation_service.go

@@ -0,0 +1,30 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package federation
+
+import (
+	"context"
+	"net/http"
+
+	fm "code.gitea.io/gitea/modules/forgefed"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/validation"
+)
+
+// ProcessLikeActivity receives a ForgeLike activity and does the following:
+// Validation of the activity
+// Creation of a (remote) federationHost if not existing
+// Creation of a forgefed Person if not existing
+// Validation of incoming RepositoryID against Local RepositoryID
+// Star the repo if it wasn't already stared
+// Do some mitigation against out of order attacks
+func ProcessLikeActivity(ctx context.Context, form any, repositoryID int64) (int, string, error) {
+	activity := form.(*fm.ForgeLike)
+	if res, err := validation.IsValid(activity); !res {
+		return http.StatusNotAcceptable, "Invalid activity", err
+	}
+	log.Info("Activity validated:%v", activity)
+
+	return 0, "", nil
+}