GraphQL Security Skill

Protect your GraphQL APIs from attacks

Overview

Learn essential security patterns for GraphQL: JWT authentication, role-based authorization, rate limiting, query complexity limits, and input validation.

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Security Checklist

Check	Priority	Implementation
Authentication	Critical	JWT with refresh tokens
Authorization	Critical	Field-level with graphql-shield
Rate Limiting	Critical	Per-user/IP with Redis
Query Depth	High	graphql-depth-limit
Query Complexity	High	graphql-query-complexity
Introspection	High	Disable in production
Input Validation	High	Validate all inputs
Error Masking	Medium	Hide internal errors

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Core Patterns

1. JWT Authentication

import jwt from 'jsonwebtoken';

// Token creation
function createTokens(user) {
  const accessToken = jwt.sign(
    { userId: user.id, roles: user.roles },
    process.env.JWT_SECRET,
    { expiresIn: '15m' }
  );

  const refreshToken = jwt.sign(
    { userId: user.id },
    process.env.JWT_REFRESH_SECRET,
    { expiresIn: '7d' }
  );

  return { accessToken, refreshToken };
}

// Context setup
const context = async ({ req }) => {
  const token = req.headers.authorization?.replace('Bearer ', '');

  let user = null;
  if (token) {
    try {
      const payload = jwt.verify(token, process.env.JWT_SECRET);
      user = await db.users.findById(payload.userId);
    } catch (e) {
      // Token invalid or expired
    }
  }

  return { user };
};

// Login resolver
const resolvers = {
  Mutation: {
    login: async (_, { email, password }) => {
      const user = await db.users.findByEmail(email);

      if (!user || !await bcrypt.compare(password, user.passwordHash)) {
        throw new GraphQLError('Invalid credentials', {
          extensions: { code: 'UNAUTHORIZED' }
        });
      }

      return { ...createTokens(user), user };
    },
  },
};

2. Authorization with graphql-shield

import { rule, shield, and, or } from 'graphql-shield';

// Rules
const isAuthenticated = rule()((_, __, { user }) => user !== null);

const isAdmin = rule()((_, __, { user }) =>
  user?.roles?.includes('ADMIN')
);

const isOwner = rule()(async (_, { id }, { user, dataSources }) => {
  const resource = await dataSources.findById(id);
  return resource?.userId === user?.id;
});

// Permissions
const permissions = shield({
  Query: {
    me: isAuthenticated,
    users: and(isAuthenticated, isAdmin),
    user: and(isAuthenticated, or(isOwner, isAdmin)),
  },
  Mutation: {
    updateUser: and(isAuthenticated, or(isOwner, isAdmin)),
    deleteUser: and(isAuthenticated, isAdmin),
  },
  User: {
    email: or(isOwner, isAdmin),
    privateField: isOwner,
  },
}, {
  fallbackError: new GraphQLError('Not authorized'),
});

// Apply
import { applyMiddleware } from 'graphql-middleware';
const protectedSchema = applyMiddleware(schema, permissions);

3. Rate Limiting

// Express-level (basic)
import rateLimit from 'express-rate-limit';

app.use('/graphql', rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100,
  keyGenerator: (req) => req.user?.id || req.ip,
}));

// GraphQL-level (granular)
const typeDefs = gql`
  directive @rateLimit(max: Int!, window: String!) on FIELD_DEFINITION

  type Mutation {
    login(email: String!, password: String!): AuthPayload!
      @rateLimit(max: 5, window: "15m")

    sendEmail(input: SendEmailInput!): Boolean!
      @rateLimit(max: 10, window: "1h")
  }
`;

4. Query Limits

import depthLimit from 'graphql-depth-limit';
import { createComplexityLimitRule } from 'graphql-validation-complexity';

const server = new ApolloServer({
  typeDefs,
  resolvers,
  validationRules: [
    // Max depth of 10
    depthLimit(10),

    // Max complexity of 1000
    createComplexityLimitRule(1000, {
      scalarCost: 1,
      objectCost: 2,
      listFactor: 10,
    }),
  ],

  // Disable introspection in production
  introspection: process.env.NODE_ENV !== 'production',
});

5. Input Validation

import validator from 'validator';
import xss from 'xss';

const validate = {
  email: (v) => {
    if (!validator.isEmail(v)) throw new Error('Invalid email');
    return validator.normalizeEmail(v);
  },

  password: (v) => {
    if (v.length < 8) throw new Error('Password too short');
    if (!/[A-Z]/.test(v)) throw new Error('Need uppercase');
    if (!/[0-9]/.test(v)) throw new Error('Need number');
    return v;
  },

  html: (v) => xss(v),
};

const resolvers = {
  Mutation: {
    createUser: async (_, { input }) => {
      const clean = {
        email: validate.email(input.email),
        password: validate.password(input.password),
        bio: input.bio ? validate.html(input.bio) : null,
      };
      return db.users.create(clean);
    },
  },
};

6. Error Masking

const server = new ApolloServer({
  formatError: (error) => {
    // Log full error
    console.error(error);

    // In production, hide internal errors
    if (process.env.NODE_ENV === 'production') {
      if (error.extensions?.code === 'INTERNAL_SERVER_ERROR') {
        return { message: 'Internal error', extensions: { code: 'INTERNAL_ERROR' } };
      }
    }

    return error;
  },
});

---

Security Headers

import helmet from 'helmet';
import cors from 'cors';

app.use(helmet());
app.use(cors({
  origin: process.env.ALLOWED_ORIGINS?.split(','),
  credentials: true,
}));
app.use(express.json({ limit: '100kb' }));

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Troubleshooting

Issue	Cause	Solution
Token always invalid	Clock skew	Add grace period
Rate limit bypass	Wrong key	Use user ID when authenticated
Auth not working	Context async	Await context setup
Introspection exposed	Wrong env check	Verify NODE_ENV

Security Testing

# Test introspection (should fail in prod)
curl -X POST $API \
  -H "Content-Type: application/json" \
  -d '{"query":"{ __schema { types { name } } }"}'

# Test rate limit
for i in {1..20}; do
  curl -X POST $API \
    -d '{"query":"mutation { login(email:\"x\",password:\"y\") { token } }"}'
done

# Test depth limit (should fail)
curl -X POST $API \
  -d '{"query":"{ user { posts { author { posts { author { id } } } } } }"}'

---

Usage

Skill("graphql-security")

Related Skills

• graphql-apollo-server - Server configuration
• graphql-resolvers - Auth in resolvers
• graphql-schema-design - Auth-aware schema

Related Agent

• 06-graphql-security - For detailed guidance