A class that ensures preconditions for a given route are respected.

Policies let you regulate routing for authentication or permissions-based reasons. This allows you to write authentication code in one place, use it in the router and not have to burden the rest of the codebase with it.

A Policy can also be used as a guard for a particular Controller action. For instance, you developed a REST API and you have a sub-resource, a policy can be created to ensure the parent exists.

Definition

• Library: tramway-core-router
• File: https://github.com/tramwayjs/router/blob/master/src/core/policies/Policy.js

Locations

• Implementation: src/policies
• Dependency Injection: src/config/services/policies.js

API

To create a policy, extend the class.

import { policies } from 'tramway-core-router';
const { Policy } = policies;

To write an authentication policy, import the class and implement the stubs.

import { policies } from 'tramway-core-router';
const { AuthenticationStrategy } = policies;

Example

import { policies, errors } from "tramway-core-router";
const { Policy } = policies;
const { HttpNotFoundError, HttpInternalServerError } = errors;
export default class ProductPolicy extends Policy {
    constructor(productService, logger) {
        this.productService = productService;
        this.logger = logger;
    }
    async check(request) {
        let product;
        const {productId} = request.params || {};
        try {
            product = await this.productService.getOne(productId);
        } catch(e) {
            this.logger.error(e.stack);
            throw new HttpInternalServerError();
        }
        if (!product) {
            throw new HttpNotFoundError();
        }
        return { product };
    }
}

Dependency Injection

import {
    ProductPolicy
} from '../../policies';
export default {
    "policy.product": {
        "class": ProductPolicy,
        "constructor": [
            {"type": "service", "key": "service.product"},
            {"type": "service", "key": "logger"},
        ]
    }
}