func newUndertakerAPI(st State, resources facade.Resources, authorizer facade.Authorizer) (*UndertakerAPI, error) {
	if !authorizer.AuthMachineAgent() || !authorizer.AuthModelManager() {
		return nil, common.ErrPerm
	}
	model, err := st.Model()
	if err != nil {
		return nil, errors.Trace(err)
	}
	getCanModifyModel := func() (common.AuthFunc, error) {
		return func(tag names.Tag) bool {
			if st.IsController() {
				return true
			}
			// Only the agent's model can be modified.
			modelTag, ok := tag.(names.ModelTag)
			if !ok {
				return false
			}
			return modelTag.Id() == model.UUID()
		}, nil
	}
	return &UndertakerAPI{
		st:           st,
		resources:    resources,
		StatusSetter: common.NewStatusSetter(st, getCanModifyModel),
	}, nil
}

// NewMetricsManagerAPI creates a new API endpoint for calling metrics manager functions.
func NewMetricsManagerAPI(
	st *state.State,
	resources facade.Resources,
	authorizer facade.Authorizer,
	clock clock.Clock,
) (*MetricsManagerAPI, error) {
	if !(authorizer.AuthMachineAgent() && authorizer.AuthModelManager()) {
		return nil, common.ErrPerm
	}

	// Allow access only to the current environment.
	accessEnviron := func() (common.AuthFunc, error) {
		return func(tag names.Tag) bool {
			if tag == nil {
				return false
			}
			return tag == st.ModelTag()
		}, nil
	}

	return &MetricsManagerAPI{
		state:         st,
		accessEnviron: accessEnviron,
		clock:         clock,
	}, nil
}

// NewUpgraderAPI creates a new server-side UpgraderAPI facade.
func NewUpgraderAPI(
	st *state.State,
	resources facade.Resources,
	authorizer facade.Authorizer,
) (*UpgraderAPI, error) {
	if !authorizer.AuthMachineAgent() {
		return nil, common.ErrPerm
	}
	getCanReadWrite := func() (common.AuthFunc, error) {
		return authorizer.AuthOwner, nil
	}
	env, err := st.Model()
	if err != nil {
		return nil, err
	}
	urlGetter := common.NewToolsURLGetter(env.UUID(), st)
	configGetter := stateenvirons.EnvironConfigGetter{st}
	return &UpgraderAPI{
		ToolsGetter: common.NewToolsGetter(st, configGetter, st, urlGetter, getCanReadWrite),
		ToolsSetter: common.NewToolsSetter(st, getCanReadWrite),
		st:          st,
		resources:   resources,
		authorizer:  authorizer,
	}, nil
}

// NewClient creates a new instance of the Client Facade.
func NewClient(
	st Backend,
	modelConfigAPI *modelconfig.ModelConfigAPI,
	resources facade.Resources,
	authorizer facade.Authorizer,
	statusSetter *common.StatusSetter,
	toolsFinder *common.ToolsFinder,
	newEnviron func() (environs.Environ, error),
	blockChecker *common.BlockChecker,
) (*Client, error) {
	if !authorizer.AuthClient() {
		return nil, common.ErrPerm
	}
	client := &Client{
		modelConfigAPI,
		&API{
			stateAccessor: st,
			auth:          authorizer,
			resources:     resources,
			statusSetter:  statusSetter,
			toolsFinder:   toolsFinder,
		},
		newEnviron,
		blockChecker,
	}
	return client, nil
}

// NewLogForwardingAPI creates a new server-side logger API end point.
func NewLogForwardingAPI(st LogForwardingState, auth facade.Authorizer) (*LogForwardingAPI, error) {
	if !auth.AuthMachineAgent() { // the controller's machine agent
		return nil, common.ErrPerm
	}
	api := &LogForwardingAPI{
		state: st,
	}
	return api, nil
}

// NewFacade creates a new authorized Facade.
func NewFacade(backend Backend, res facade.Resources, auth facade.Authorizer) (*Facade, error) {
	if !auth.AuthModelManager() {
		return nil, common.ErrPerm
	}
	return &Facade{
		backend:   backend,
		resources: res,
	}, nil
}

// New creates a Facade backed by backend and resources. If auth
// doesn't identity the client as a machine agent or a unit agent,
// it will return common.ErrPerm.
func New(backend Backend, resources facade.Resources, auth facade.Authorizer) (*Facade, error) {
	if !auth.AuthMachineAgent() && !auth.AuthUnitAgent() {
		return nil, common.ErrPerm
	}
	return &Facade{
		backend:   backend,
		resources: resources,
	}, nil
}

// NewInstancePollerAPI creates a new server-side InstancePoller API
// facade.
func NewInstancePollerAPI(
	st *state.State,
	resources facade.Resources,
	authorizer facade.Authorizer,
	clock clock.Clock,
) (*InstancePollerAPI, error) {

	if !authorizer.AuthModelManager() {
		// InstancePoller must run as environment manager.
		return nil, common.ErrPerm
	}
	accessMachine := common.AuthFuncForTagKind(names.MachineTagKind)
	sti := getState(st)

	// Life() is supported for machines.
	lifeGetter := common.NewLifeGetter(
		sti,
		accessMachine,
	)
	// ModelConfig() and WatchForModelConfigChanges() are allowed
	// with unrestriced access.
	modelWatcher := common.NewModelWatcher(
		sti,
		resources,
		authorizer,
	)
	// WatchModelMachines() is allowed with unrestricted access.
	machinesWatcher := common.NewModelMachinesWatcher(
		sti,
		resources,
		authorizer,
	)
	// InstanceId() is supported for machines.
	instanceIdGetter := common.NewInstanceIdGetter(
		sti,
		accessMachine,
	)
	// Status() is supported for machines.
	statusGetter := common.NewStatusGetter(
		sti,
		accessMachine,
	)

	return &InstancePollerAPI{
		LifeGetter:           lifeGetter,
		ModelWatcher:         modelWatcher,
		ModelMachinesWatcher: machinesWatcher,
		InstanceIdGetter:     instanceIdGetter,
		StatusGetter:         statusGetter,
		st:                   sti,
		resources:            resources,
		authorizer:           authorizer,
		accessMachine:        accessMachine,
		clock:                clock,
	}, nil
}

// NewFacade returns a singular-controller API facade, backed by the supplied
// state, so long as the authorizer represents a controller machine.
func NewFacade(backend Backend, auth facade.Authorizer) (*Facade, error) {
	if !auth.AuthModelManager() {
		return nil, common.ErrPerm
	}
	return &Facade{
		auth:    auth,
		model:   backend.ModelTag(),
		claimer: backend.SingularClaimer(),
	}, nil
}

func NewDiscoverSpacesAPIWithBacking(st networkingcommon.NetworkBacking, resources facade.Resources, authorizer facade.Authorizer) (*DiscoverSpacesAPI, error) {
	if !authorizer.AuthModelManager() {
		return nil, common.ErrPerm
	}
	return &DiscoverSpacesAPI{
		st:         st,
		authorizer: authorizer,
		resources:  resources,
	}, nil
}

// NewAPIWithBacking creates a new server-side API facade with the given Backing.
func NewAPIWithBacking(st Backend, resources facade.Resources, authorizer facade.Authorizer) (*ProxyUpdaterAPI, error) {
	if !(authorizer.AuthMachineAgent() || authorizer.AuthUnitAgent()) {
		return &ProxyUpdaterAPI{}, common.ErrPerm
	}
	return &ProxyUpdaterAPI{
		backend:    st,
		resources:  resources,
		authorizer: authorizer,
	}, nil
}

// NewLoggerAPI creates a new server-side logger API end point.
func NewLoggerAPI(
	st *state.State,
	resources facade.Resources,
	authorizer facade.Authorizer,
) (*LoggerAPI, error) {
	if !authorizer.AuthMachineAgent() && !authorizer.AuthUnitAgent() {
		return nil, common.ErrPerm
	}
	return &LoggerAPI{state: st, resources: resources, authorizer: authorizer}, nil
}

// newAPIWithBacking creates a new server-side Spaces API facade with
// the given Backing.
func newAPIWithBacking(backing networkingcommon.NetworkBacking, resources facade.Resources, authorizer facade.Authorizer) (API, error) {
	// Only clients can access the Spaces facade.
	if !authorizer.AuthClient() {
		return nil, common.ErrPerm
	}
	return &spacesAPI{
		backing:    backing,
		resources:  resources,
		authorizer: authorizer,
	}, nil
}

// NewCharmRevisionUpdaterAPI creates a new server-side charmrevisionupdater API end point.
func NewCharmRevisionUpdaterAPI(
	st *state.State,
	resources facade.Resources,
	authorizer facade.Authorizer,
) (*CharmRevisionUpdaterAPI, error) {
	if !authorizer.AuthMachineAgent() && !authorizer.AuthModelManager() {
		return nil, common.ErrPerm
	}
	return &CharmRevisionUpdaterAPI{
		state: st, resources: resources, authorizer: authorizer}, nil
}

// NewModelConfigAPI creates a new instance of the ModelConfig Facade.
func NewModelConfigAPI(backend Backend, authorizer facade.Authorizer) (*ModelConfigAPI, error) {
	if !authorizer.AuthClient() {
		return nil, common.ErrPerm
	}
	client := &ModelConfigAPI{
		backend: backend,
		auth:    authorizer,
		check:   common.NewBlockChecker(backend),
	}
	return client, nil
}

// NewHighAvailabilityAPI creates a new server-side highavailability API end point.
func NewHighAvailabilityAPI(st *state.State, resources facade.Resources, authorizer facade.Authorizer) (*HighAvailabilityAPI, error) {
	// Only clients and environment managers can access the high availability service.
	if !authorizer.AuthClient() && !authorizer.AuthModelManager() {
		return nil, common.ErrPerm
	}
	return &HighAvailabilityAPI{
		state:      st,
		resources:  resources,
		authorizer: authorizer,
	}, nil
}

// NewImageManagerAPI creates a new server-side imagemanager API end point.
func NewImageManagerAPI(st *state.State, resources facade.Resources, authorizer facade.Authorizer) (*ImageManagerAPI, error) {
	// Only clients can access the image manager service.
	if !authorizer.AuthClient() {
		return nil, common.ErrPerm
	}
	return &ImageManagerAPI{
		state:      getState(st),
		resources:  resources,
		authorizer: authorizer,
		check:      common.NewBlockChecker(st),
	}, nil
}

func checkAuth(authorizer facade.Authorizer, st *state.State) error {
	if !authorizer.AuthClient() {
		return errors.Trace(common.ErrPerm)
	}

	if isAdmin, err := authorizer.HasPermission(permission.SuperuserAccess, st.ControllerTag()); err != nil {
		return errors.Trace(err)
	} else if !isAdmin {
		// The entire facade is only accessible to controller administrators.
		return errors.Trace(common.ErrPerm)
	}
	return nil
}

// NewCleanerAPI creates a new instance of the Cleaner API.
func NewCleanerAPI(
	st *state.State,
	res facade.Resources,
	authorizer facade.Authorizer,
) (*CleanerAPI, error) {
	if !authorizer.AuthModelManager() {
		return nil, common.ErrPerm
	}
	return &CleanerAPI{
		st:        getState(st),
		resources: res,
	}, nil
}

// NewLeadershipService constructs a new LeadershipService.
func NewLeadershipService(
	claimer leadership.Claimer, authorizer facade.Authorizer,
) (LeadershipService, error) {

	if !authorizer.AuthUnitAgent() {
		return nil, errors.Unauthorizedf("permission denied")
	}

	return &leadershipService{
		claimer:    claimer,
		authorizer: authorizer,
	}, nil
}