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Improve @auth example and corresponding tests.
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@benjamn
benjamn committed Mar 14, 2018
1 parent 63cec8e commit 9b29251
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50 changes: 28 additions & 22 deletions docs/source/schema-directives.md
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Original file line number Diff line number Diff line change
Expand Up @@ -270,10 +270,9 @@ GraphQL is great for internationalization, since a GraphQL server can access unl

### Enforcing access permissions

To implement the `@auth` example mentioned in the [**Declaring schema directives**](schema-directives.html#Declaring-schema-directives) section below:
Imagine a hypothetical `@auth` directive that takes an argument `requires` of type `Role`, which defaults to `ADMIN`. This `@auth` directive can appear on an `OBJECT` like `User` to set default access permissions for all `User` fields, as well as appearing on individual fields, to enforce field-specific `@auth` restrictions:

```js
const typeDefs = `
```gql
directive @auth(
requires: Role = ADMIN,
) on OBJECT | FIELD_DEFINITION
Expand All @@ -289,52 +288,57 @@ type User @auth(requires: USER) {
name: String
banned: Boolean @auth(requires: ADMIN)
canPost: Boolean @auth(requires: REVIEWER)
}`;
}
```

// Symbols can be a good way to store semi-hidden data on schema objects.
const authRoleSymbol = Symbol.for("@auth role");
const authWrapSymbol = Symbol.for("@auth wrapped");
What makes this example tricky is that the `OBJECT` version of the directive needs to wrap all fields of the object, even though some of those fields may be individually wrapped by `@auth` directives at the `FIELD_DEFINITION` level, and we would prefer not to rewrap resolvers if we can help it:

```js
class AuthDirective extends SchemaDirectiveVisitor {
visitObject(type) {
this.ensureFieldsWrapped(type);
type[authRoleSymbol] = this.args.requires;
type._requiredAuthRole = this.args.requires;
}

// Visitor methods for nested types like fields and arguments
// also receive a details object that provides information about
// the parent and grandparent types.
visitFieldDefinition(field, details) {
this.ensureFieldsWrapped(details.objectType);
field[authRoleSymbol] = this.args.requires;
field._requiredAuthRole = this.args.requires;
}

ensureFieldsWrapped(type) {
// Mark the GraphQLObjectType object to avoid re-wrapping its fields:
if (type[authWrapSymbol]) {
return;
}
ensureFieldsWrapped(objectType) {
// Mark the GraphQLObjectType object to avoid re-wrapping:
if (objectType._authFieldsWrapped) return;
objectType._authFieldsWrapped = true;

const fields = objectType.getFields();

const fields = type.getFields();
Object.keys(fields).forEach(fieldName => {
const field = fields[fieldName];
const { resolve = defaultFieldResolver } = field;
field.resolve = async function (...args) {
// Get the required role from the field first, falling back to the
// parent GraphQLObjectType if no role is required by the field:
const requiredRole = field[authRoleSymbol] || type[authRoleSymbol];
// Get the required Role from the field first, falling back
// to the objectType if no Role is required by the field:
const requiredRole =
field._requiredAuthRole ||
objectType._requiredAuthRole;

if (! requiredRole) {
return resolve.apply(this, args);
}

const context = args[2];
const user = await getUser(context.headers.authToken);
if (! user.hasRole(requiredRole)) {
throw new Error("not authorized");
}

return resolve.apply(this, args);
};
});

type[authWrapSymbol] = true;
}
};
}

const schema = makeExecutableSchema({
typeDefs,
Expand All @@ -346,6 +350,8 @@ const schema = makeExecutableSchema({
});
```

One drawback of this approach is that it does not guarantee fields will be wrapped if they are added to the schema after `AuthDirective` is applied, and the whole `getUser(context.headers.authToken)` is a made-up API that would need to be fleshed out. In other words, we’ve glossed over some of the details that would be required for a production-ready implementation of this directive, though we hope the basic structure shown here inspires you to find clever solutions to the remaining problems.

### Enforcing value restrictions

Suppose you want to enforce a maximum length for a string-valued field:
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96 changes: 52 additions & 44 deletions src/test/testDirectives.ts
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Expand Up @@ -678,8 +678,6 @@ describe('@directives', () => {
});

it('can be used to implement the @auth example', async () => {
const authReqSymbol = Symbol.for('@auth required role');
const authWrapSymbol = Symbol.for('@auth wrapped');
const roles = [
'UNKNOWN',
'USER',
Expand All @@ -697,6 +695,57 @@ describe('@directives', () => {
};
}

class AuthDirective extends SchemaDirectiveVisitor {
public visitObject(type: GraphQLObjectType) {
this.ensureFieldsWrapped(type);
(type as any)._requiredAuthRole = this.args.requires;
}
// Visitor methods for nested types like fields and arguments
// also receive a details object that provides information about
// the parent and grandparent types.
public visitFieldDefinition(
field: GraphQLField<any, any>,
details: { objectType: GraphQLObjectType },
) {
this.ensureFieldsWrapped(details.objectType);
(field as any)._requiredAuthRole = this.args.requires;
}

public ensureFieldsWrapped(objectType: GraphQLObjectType) {
// Mark the GraphQLObjectType object to avoid re-wrapping:
if ((objectType as any)._authFieldsWrapped) {
return;
}
(objectType as any)._authFieldsWrapped = true;

const fields = objectType.getFields();

Object.keys(fields).forEach(fieldName => {
const field = fields[fieldName];
const { resolve = defaultFieldResolver } = field;
field.resolve = async function (...args: any[]) {
// Get the required Role from the field first, falling back
// to the objectType if no Role is required by the field:
const requiredRole =
(field as any)._requiredAuthRole ||
(objectType as any)._requiredAuthRole;

if (! requiredRole) {
return resolve.apply(this, args);
}

const context = args[2];
const user = await getUser(context.headers.authToken);
if (! user.hasRole(requiredRole)) {
throw new Error('not authorized');
}

return resolve.apply(this, args);
};
});
}
}

const schema = makeExecutableSchema({
typeDefs: `
directive @auth(
Expand All @@ -721,48 +770,7 @@ describe('@directives', () => {
}`,

directives: {
auth: class extends SchemaDirectiveVisitor {
public visitObject(type: GraphQLObjectType) {
this.ensureFieldsWrapped(type);
type[authReqSymbol] = this.args.requires;
}

public visitFieldDefinition(field: GraphQLField<any, any>, details: {
objectType: GraphQLObjectType,
}) {
this.ensureFieldsWrapped(details.objectType);
field[authReqSymbol] = this.args.requires;
}

private ensureFieldsWrapped(type: GraphQLObjectType) {
// Mark the GraphQLObjectType object to avoid re-wrapping its fields:
if (type[authWrapSymbol]) {
return;
}

const fields = type.getFields();
Object.keys(fields).forEach(fieldName => {
const field = fields[fieldName];
const { resolve = defaultFieldResolver } = field;
field.resolve = async function (...args: any[]) {
// Get the required role from the field first, falling back to the
// parent GraphQLObjectType if no role is required by the field:
const requiredRole = field[authReqSymbol] || type[authReqSymbol];
if (! requiredRole) {
return resolve.apply(this, args);
}
const context = args[2];
const user = await getUser(context.headers.authToken);
if (! user.hasRole(requiredRole)) {
throw new Error('not authorized');
}
return resolve.apply(this, args);
};
});

type[authWrapSymbol] = true;
}
}
auth: AuthDirective
},

resolvers: {
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