feat(context): add @inject.binding and improve @inject.setter

1. The decorators now allow binding creation policy control
2. `@inject.binding` can be used to resolve/configure a binding

docs/site/Decorators_inject.md

@@ -126,7 +126,19 @@ class MyControllerWithGetter {
 
 `@inject.setter` injects a setter function to set the bound value of the key.
 
-Syntax: `@inject.setter(bindingKey: string)`.
+Syntax: `@inject.setter(bindingKey: BindingAddress, {bindingCreation?: ...})`.
+
+The `setter` function injected has the following signature:
+
+```ts
+export type Setter<T> = (value?: T) => void;
+```
+
+The binding resolution/creation is controlled by `bindingCreation` option. See
+[@inject.binding](#injectbinding) for possible settings.
+
+The following example shows the usage of `@inject.setter` and the injected
+setter function.
 
 ```ts
 export class HelloController {
@@ -143,6 +155,70 @@ export class HelloController {
 }
 ```
 
+Please note the setter function simply binds a `value` to the underlying binding
+using `binding.to(value)`.
+
+To set other types of value providers such as `toDynamicValue`or `toClass`, use
+`@inject.binding` instead.
+
+### @inject.binding
+
+`@inject.binding` injects a binding for the given key. It can be used to bind
+various types of value providers to the underlying binding or configure the
+binding. This is an advanced form of `@inject.setter`, which only allows to set
+a constant value (using `Binding.to(value)` behind the scene) to the underlying
+binding.
+
+Syntax: `@inject.binding(bindingKey: BindingAddress, {bindingCreation?: ...})`.
+
+```ts
+export class HelloController {
+  constructor(
+    @inject.binding('greeting') private greetingBinding: Binding<string>,
+  ) {}
+
+  @get('/hello')
+  async greet() {
+    // Bind `greeting` to a factory function that reads default greeting
+    // from a file or database
+    this.greetingBinding.toDynamicValue(() => readDefaultGreeting());
+    return await this.greetingBinding.get<string>(this.greetingBinding.key);
+  }
+}
+```
+
+The `@inject.binding` takes an optional `metadata` object which can contain
+`bindingCreation` to control how underlying binding is resolved or created based
+on the following values:
+
+```ts
+/**
+ * Policy to control if a binding should be created for the context
+ */
+export enum BindingCreationPolicy {
+  /**
+   * Always create a binding with the key for the context
+   */
+  ALWAYS_CREATE = 'Always',
+  /**
+   * Never create a binding for the context. If the key is not bound in the
+   * context, throw an error.
+   */
+  NEVER_CREATE = 'Never',
+  /**
+   * Create a binding if the key is not bound in the context. Otherwise, return
+   * the existing binding.
+   */
+  CREATE_IF_NOT_BOUND = 'IfNotBound',
+}
+```
+
+For example:
+
+```ts
+@inject.setter('binding-key', {bindingCreation: BindingCreationPolicy.NEVER_CREATES})
+```
+
 ### @inject.tag
 
 `@inject.tag` injects an array of values by a pattern or regexp to match binding

docs/site/Dependency-injection.md

@@ -245,6 +245,7 @@ There are a few special decorators from the `inject` namespace.
 
 - [`@inject.getter`](Decorators_inject.md#@inject.getter)
 - [`@inject.setter`](Decorators_inject.md#@inject.setter)
+- [`@inject.binding`](Decorators_inject.md#@inject.binding)
 - [`@inject.context`](Decorators_inject.md#@inject.context)
 - [`@inject.tag`](Decorators_inject.md#@inject.tag)
 - [`@inject.view`](Decorators_inject.md#@inject.view)

packages/authentication/src/__tests__/unit/providers/authentication.provider.unit.ts

@@ -3,13 +3,13 @@
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
 
-import {expect} from '@loopback/testlab';
 import {Context, instantiateClass} from '@loopback/context';
 import {Request} from '@loopback/rest';
-import {AuthenticateFn, UserProfile, AuthenticationBindings} from '../../..';
-import {MockStrategy} from '../fixtures/mock-strategy';
+import {expect} from '@loopback/testlab';
 import {Strategy} from 'passport';
+import {AuthenticateFn, AuthenticationBindings, UserProfile} from '../../..';
 import {AuthenticateActionProvider} from '../../../providers';
+import {MockStrategy} from '../fixtures/mock-strategy';
 
 describe('AuthenticateActionProvider', () => {
   describe('constructor()', () => {