nexus-shield

Help Wanted ⚠️

If you are a Typescript expert, I could use a hand on a lingering typing issue when a shield parameter is added to an objectType. Please see the related issue for details. Thanks!

Overview

Nexus Shield is a nexus plugin that helps you create an authorization layer for your application. It is a replacement for the provided authorization plugin. It is heavily inspired by Graphql Shield and reuses most of its familiar ruling system. It takes full advantage of the type safety provided by nexus.

Install

npm install --save nexus-shield

OR

yarn add nexus-shield

Usage

Nexus configuration

The plugin first needs to be installed in nexus. This will add the new shield parameter. The plugin will work without any provided configuration, but it is recommended to provide one that is relevant to your application. The available parameters are:

• defaultError: The error that is thrown if the access is denied. See the errors section.
• defaultRule: Rule that is used if none is specified for a field.
• hashFunction: Function used to hash the input to provide caching keys.

For example, using an Apollo server:

import { nexusShield, allow } from 'nexus-shield';
import { ForbiddenError } from 'apollo-server';

const schema = makeSchema({
  // ... Rest of the configuration
  plugins: [
    nexusShield({
      defaultError: new ForbiddenError('Not allowed'),
      defaultRule: allow,
    }),
  ],
});

Subscriptions configuration

• When using subscriptions with a server that is not integrated directly into your "main" GraphQL server, you must make sure that you pass in a valid context.
• This context should contain all the information needed to evaluate the rules. Ideally, it is the same as the context for your "main" server otherwise the typing won't reflect the data available to the rules.

For example, using GraphQL-WS:

useServer(
  {
    schema,
    context: (ctx, msg, args) => {
      // That will return the same context that was passed when the
      // server received the subscription request
      return ctx;
    },
  },
  wsServer
);

Styles

Two interface styles are provided for convenience: Graphql-Shield and Nexus.

Graphql-Shield

rule()((root, args, ctx) => {
  return !!ctx.user;
});

Nexus

ruleType({
  resolve: (root, args, ctx) => {
    return !!ctx.user;
  },
});

Error

• A rule needs to return a boolean, a Promise<boolean> or throw an Error.
• Contrary to Graphql-shield, this plugin will NOT catch the errors you throw and will just pass them down to the next plugins and eventually to the server
• If false is returned, the configured defaultError will be thrown by the plugin.

import { AuthenticationError } from 'apollo-server';

const isAuthenticated = ruleType({
  resolve: (root, args, ctx) => {
    const allowed = !!ctx.user;
    if (!allowed) throw new AuthenticationError('Bearer token required');
    return allowed;
  },
});

Operators

Rules can be combined in a very flexible manner. The plugin provides the following operators:

• and: Returns true if all rules return true
• or: Returns true if one rule returns true
• not: Inverts the result of a rule
• chain: Same as and, but rules are executed in order
• race: Same as or, but rules are executed in order
• deny: Returns false
• allow: Returns true

Simple example:

import { chain, not, ruleType } from 'nexus-shield';

const hasScope = (scope: string) => {
  return ruleType({
    resolve: (root, args, ctx) => {
      return ctx.user.permissions.includes(scope);
    },
  });
};

const backlist = ruleType({
  resolve: (root, args, ctx) => {
    return ctx.user.token === 'some-token';
  },
});

const viewerIsAuthorized = chain(
  isAuthenticated,
  not(backlist),
  hasScope('products:read')
);

Shield Parameter

To use a rule, it must be assigned to the shield parameter of a field:

export const Product = objectType({
  name: 'Product',
  definition(t) {
    t.id('id');
    t.string('prop', {
      shield: ruleType({
        resolve: (root, args, ctx) => {
          return !!ctx.user;
        },
      }),
    });
  },
});

Type safety

This plugin will try its best to provide typing to the rules.

• It is preferable to define rules directly in the definition to have access to the full typing of root and args.
• The ctx is always typed if it was properly configured in nexus makeSchema.
• If creating generic or partial rules, use the appropriate helpers (see below).

export type Context = {
  user?: { id: string };
};

export const Product = objectType({
  name: 'Product',
  definition(t) {
    t.id('id');
    t.string('ownerId');
    t.string('prop', {
      args: {
        filter: stringArg({ nullable: false }),
      },
      shield: ruleType({
        resolve: (root, args, ctx) => {
          // root => { id: string }, args => { filter: string }, ctx => Context
          return true;
        },
      }),
    });
  },
});

Generic rules

• Generic rules are rules that do not depend on the type of the root or args.
• The wrapper generic is provided for this purpose. It will wrap your rule in a generic function.

const isAuthenticated = generic(
  ruleType({
    resolve: (root, args, ctx) => {
      // Only ctx is typed
      return !!ctx.user;
    },
  })
);

// Usage
t.string('prop', {
  shield: isAuthenticated(),
});

Partial rules

• Partial rules are rules that depend only on the type of the root.
• The wrapper partial is provided for this purpose. It will wrap your rule in a generic function.

const viewerIsOwner = partial(
  ruleType({
    type: 'Product' // It is also possible to use the generic parameter of `partial`
    resolve: (root, args, ctx) => {
      // Both root and ctx are typed
      return root.ownerId === ctx.user.id;
    },
  })
);

// Usage
t.string('prop', {
  shield: viewerIsOwner(),
});

Combining rules

If you mix and match generic rules with partial rules, you will need to specify the type in the parent helper.

const viewerIsAuthorized = partial<'Product'>(
  chain(isAuthenticated(), viewerIsOwner())
);

However, if you specify it directly in the shield field, there is no need for a helper thus no need for a parameter.

t.string('prop', {
  shield: chain(isAuthenticated(), viewerIsOwner()),
});

Caching

• The result of a rule can be cached to maximize performance. This is important when using generic or partial rules that require access to external data.
• The caching is always scoped to the request

The plugin offers 3 levels of caching:

• NO_CACHE: No caching is done (default)
• CONTEXTUAL: Use when the rule only depends on the ctx
• STRICT: Use when the rule depends on the root or args

Usage:

rule({ cache: ShieldCache.STRICT })((root, args, ctx) => {
  return true;
});

ruleType({
  cache: ShieldCache.STRICT,
  resolve: (root, args, ctx) => {
    return !!ctx.user;
  },
});

Known issues / limitations

• Currently, the typing of the shield parameter on objectType doesn't work. Tracked by issue: https://github.com/Sytten/nexus-shield/issues/50

• It is not possible to pass directly an objectType to the parameter type of a ruleType. Tracked by issue: https://github.com/graphql-nexus/schema/issues/451

• The helpers are necessary to provide strong typing and avoid the propagation of any. See this StackOverflow issue for more on the subject.