[FEAT] Allow pushmirror to use publickey authentication

- Continuation of https://github.com/go-gitea/gitea/pull/18835 (by
@Gusted, so it's fine to change copyright holder to Forgejo).
- Add the option to use SSH for push mirrors, this would allow for the
deploy keys feature to be used and not require tokens to be used which
cannot be limited to a specific repository. The private key is stored
encrypted (via the `keying` module) on the database and NEVER given to
the user, to avoid accidental exposure and misuse.
- CAVEAT: This does require the `ssh` binary to be present, which may
not be available in containerized environments, this could be solved by
adding a SSH client into forgejo itself and use the forgejo binary as
SSH command, but should be done in another PR.
- CAVEAT: Mirroring of LFS content is not supported, this would require
the previous stated problem to be solved due to LFS authentication (an
attempt was made at forgejo/forgejo#2544).
- Integration test added.
- Resolves #4416

routers/api/v1/repo/mirror.go

@@ -350,6 +350,11 @@ func CreatePushMirror(ctx *context.APIContext, mirrorOption *api.CreatePushMirro
 		return
 	}
 
+	if mirrorOption.UseSSH && (mirrorOption.RemoteUsername != "" || mirrorOption.RemotePassword != "") {
+		ctx.Error(http.StatusBadRequest, "CreatePushMirror", "'use_ssh' is mutually exclusive with 'remote_username' and 'remote_passoword'")
+		return
+	}
+
 	address, err := forms.ParseRemoteAddr(mirrorOption.RemoteAddress, mirrorOption.RemoteUsername, mirrorOption.RemotePassword)
 	if err == nil {
 		err = migrations.IsMigrateURLAllowed(address, ctx.ContextUser)
@@ -365,7 +370,7 @@ func CreatePushMirror(ctx *context.APIContext, mirrorOption *api.CreatePushMirro
 		return
 	}
 
-	remoteAddress, err := util.SanitizeURL(mirrorOption.RemoteAddress)
+	remoteAddress, err := util.SanitizeURL(address)
 	if err != nil {
 		ctx.ServerError("SanitizeURL", err)
 		return
@@ -380,11 +385,29 @@ func CreatePushMirror(ctx *context.APIContext, mirrorOption *api.CreatePushMirro
 		RemoteAddress: remoteAddress,
 	}
 
+	var plainPrivateKey []byte
+	if mirrorOption.UseSSH {
+		publicKey, privateKey, err := util.GenerateSSHKeypair()
+		if err != nil {
+			ctx.ServerError("GenerateSSHKeypair", err)
+			return
+		}
+		plainPrivateKey = privateKey
+		pushMirror.PublicKey = string(publicKey)
+	}
+
 	if err = db.Insert(ctx, pushMirror); err != nil {
 		ctx.ServerError("InsertPushMirror", err)
 		return
 	}
 
+	if mirrorOption.UseSSH {
+		if err = pushMirror.SetPrivatekey(ctx, plainPrivateKey); err != nil {
+			ctx.ServerError("SetPrivatekey", err)
+			return
+		}
+	}
+
 	// if the registration of the push mirrorOption fails remove it from the database
 	if err = mirror_service.AddPushMirrorRemote(ctx, pushMirror, address); err != nil {
 		if err := repo_model.DeletePushMirrors(ctx, repo_model.PushMirrorOptions{ID: pushMirror.ID, RepoID: pushMirror.RepoID}); err != nil {

routers/web/repo/setting/setting.go

@@ -478,8 +478,7 @@ func SettingsPost(ctx *context.Context) {
 			ctx.ServerError("UpdateAddress", err)
 			return
 		}
-
-		remoteAddress, err := util.SanitizeURL(form.MirrorAddress)
+		remoteAddress, err := util.SanitizeURL(address)
 		if err != nil {
 			ctx.ServerError("SanitizeURL", err)
 			return
@@ -638,6 +637,12 @@ func SettingsPost(ctx *context.Context) {
 			return
 		}
 
+		if form.PushMirrorUseSSH && (form.PushMirrorUsername != "" || form.PushMirrorPassword != "") {
+			ctx.Data["Err_PushMirrorUseSSH"] = true
+			ctx.RenderWithErr(ctx.Tr("repo.mirror_denied_combination"), tplSettingsOptions, &form)
+			return
+		}
+
 		address, err := forms.ParseRemoteAddr(form.PushMirrorAddress, form.PushMirrorUsername, form.PushMirrorPassword)
 		if err == nil {
 			err = migrations.IsMigrateURLAllowed(address, ctx.Doer)
@@ -654,7 +659,7 @@ func SettingsPost(ctx *context.Context) {
 			return
 		}
 
-		remoteAddress, err := util.SanitizeURL(form.PushMirrorAddress)
+		remoteAddress, err := util.SanitizeURL(address)
 		if err != nil {
 			ctx.ServerError("SanitizeURL", err)
 			return
@@ -668,11 +673,30 @@ func SettingsPost(ctx *context.Context) {
 			Interval:      interval,
 			RemoteAddress: remoteAddress,
 		}
+
+		var plainPrivateKey []byte
+		if form.PushMirrorUseSSH {
+			publicKey, privateKey, err := util.GenerateSSHKeypair()
+			if err != nil {
+				ctx.ServerError("GenerateSSHKeypair", err)
+				return
+			}
+			plainPrivateKey = privateKey
+			m.PublicKey = string(publicKey)
+		}
+
 		if err := db.Insert(ctx, m); err != nil {
 			ctx.ServerError("InsertPushMirror", err)
 			return
 		}
 
+		if form.PushMirrorUseSSH {
+			if err := m.SetPrivatekey(ctx, plainPrivateKey); err != nil {
+				ctx.ServerError("SetPrivatekey", err)
+				return
+			}
+		}
+
 		if err := mirror_service.AddPushMirrorRemote(ctx, m, address); err != nil {
 			if err := repo_model.DeletePushMirrors(ctx, repo_model.PushMirrorOptions{ID: m.ID, RepoID: m.RepoID}); err != nil {
 				log.Error("DeletePushMirrors %v", err)