How to fix MongoServerError: bad auth : authentication failed in MongoDB

// Correct format with authentication
mongodb://username:password@host:port/database?authSource=admin

// MongoDB Atlas format
mongodb+srv://username:[email protected]/database?retryWrites=true&w=majority

# Connect with explicit authentication
mongosh "mongodb://username:password@localhost:27017/mydb?authSource=admin"

# Or connect and authenticate separately
mongosh --host localhost --port 27017
use admin
db.auth("username", "password")

// If password is "pass@word#123"
const encodedPassword = encodeURIComponent("pass@word#123");
const connectionString = `mongodb://username:${encodedPassword}@localhost:27017/mydb?authSource=admin`;

mongosh --host localhost --port 27017

// Switch to admin database
use admin

// List all users
db.getUsers()

// Check specific user
db.getUser("username")

// Check user roles and privileges
db.getUser("username").roles

use admin

// Create user with read/write access to specific database
db.createUser({
  user: "username",
  pwd: "password",
  roles: [
    { role: "readWrite", db: "mydb" },
    { role: "read", db: "reporting" }
  ]
})

// Or create user with admin privileges
db.createUser({
  user: "adminUser",
  pwd: "adminPassword",
  roles: ["root"]
})

use admin
db.changeUserPassword("username", "newPassword")

// Authenticate as the user
db.auth("username", "password")

// Try to access the database
use mydb
db.test.insertOne({ test: 1 })  // Should succeed if permissions are correct

// Connect with admin privileges
use admin

// Check all databases for users
const dbs = db.adminCommand({ listDatabases: 1 }).databases;
dbs.forEach(dbInfo => {
  const dbName = dbInfo.name;
  const userCount = db.getSiblingDB(dbName).getUsers().length;
  if (userCount > 0) {
    print("Database " + dbName + " has " + userCount + " user(s)");
    db.getSiblingDB(dbName).getUsers().forEach(user => {
      print("  User: " + user.user);
    });
  }
});

// User in admin database, connecting to mydb
const uri1 = 'mongodb://username:password@localhost:27017/mydb?authSource=admin';

// User in mydb database, connecting to mydb
const uri2 = 'mongodb://username:password@localhost:27017/mydb?authSource=mydb';

// MongoDB Atlas with authSource
const uri3 = 'mongodb+srv://username:[email protected]/mydb?authSource=admin&retryWrites=true&w=majority';

// Multiple parameters
const uri4 = 'mongodb://username:password@localhost:27017/mydb?authSource=admin&authMechanism=SCRAM-SHA-256';

// Node.js MongoDB driver
const { MongoClient } = require('mongodb');

const uri = 'mongodb://username:password@localhost:27017/mydb?authSource=admin';
const client = new MongoClient(uri);

// Mongoose
const mongoose = require('mongoose');
mongoose.connect('mongodb://username:password@localhost:27017/mydb', {
  authSource: 'admin',
  authMechanism: 'SCRAM-SHA-256',
});

mongosh --eval "db.version()"

// In mongosh
db.adminCommand({ getParameter: 1, authenticationMechanisms: 1 })

// Explicitly specify SCRAM-SHA-256
const uri = 'mongodb://username:password@localhost:27017/mydb?authSource=admin&authMechanism=SCRAM-SHA-256';

// For MongoDB Atlas (usually SCRAM-SHA-256)
const atlasUri = 'mongodb+srv://username:[email protected]/mydb?authMechanism=SCRAM-SHA-256&retryWrites=true&w=majority';

// Force SCRAM-SHA-1 for compatibility
const uri = 'mongodb://username:password@localhost:27017/mydb?authSource=admin&authMechanism=SCRAM-SHA-1';

# Node.js MongoDB driver
npm install mongodb@latest

# Mongoose
npm install mongoose@latest

const { MongoClient } = require('mongodb');
console.log('Driver version:', require('mongodb/package.json').version);

# Check mongod configuration
cat /etc/mongod.conf | grep -A5 -B5 security

# Or in mongosh
db.adminCommand({ getParameter: 1, auth: 1 })

security:
  authorization: enabled  # This enables authentication
  # Other security settings...

# Linux iptables
sudo iptables -L -n | grep 27017

# Linux firewalld
sudo firewall-cmd --list-all | grep 27017

# Windows
netsh advfirewall firewall show rule name=all | findstr 27017

# Test basic connectivity
ping mongodb-host

# Test MongoDB port
nc -zv mongodb-host 27017

# Test with authentication (using mongosh)
mongosh "mongodb://username:password@mongodb-host:27017/admin?authSource=admin" --eval "db.runCommand({ping:1})"

// Connection string with SSL
const uri = 'mongodb://username:password@localhost:27017/mydb?authSource=admin&ssl=true';

// With specific SSL options (Node.js driver)
const client = new MongoClient(uri, {
  ssl: true,
  sslValidate: true,
  sslCA: fs.readFileSync('/path/to/ca.pem'),
  sslCert: fs.readFileSync('/path/to/client.pem'),
  sslKey: fs.readFileSync('/path/to/client.key'),
});

# Typical log locations
tail -f /var/log/mongodb/mongod.log
tail -f /var/log/mongodb/mongodb.log

# Docker containers
docker logs mongodb-container

// In mongosh, set log level
db.adminCommand({
  setParameter: 1,
  logLevel: 2  // 0=off, 1=error, 2=warning, 3=info, 4=debug, 5=trace
})

// Or set component-specific logging
db.adminCommand({
  setParameter: 1,
  logComponentVerbosity: {
    authentication: { verbosity: 2 }
  }
})

// Check current connections and their authentication state
db.currentOp(true).inprog.forEach(op => {
  if (op.clientMetadata) {
    print("Connection from " + op.client + ", authenticated: " + (op.clientMetadata.auth || "none"));
  }
});

// Check authentication statistics
db.serverStatus().connections
db.serverStatus().security

// Check user authentication attempts (if audit logging enabled)
use admin
db.system.audit.find({ "atype": "authenticate" }).sort({ ts: -1 }).limit(10)

# Test with mongosh
mongosh --username username --password password --authenticationDatabase admin --host localhost --port 27017

# Test with mongoimport (if applicable)
mongoimport --uri "mongodb://username:password@localhost:27017/mydb?authSource=admin" --collection test --file data.json

# Test with Compass (MongoDB GUI)
# Download MongoDB Compass and test connection visually

// test-auth.js
const { MongoClient } = require('mongodb');

async function testAuth() {
  const uri = 'mongodb://username:password@localhost:27017/mydb?authSource=admin';

  try {
    const client = new MongoClient(uri);
    await client.connect();
    console.log('Authentication successful!');

    const db = client.db('mydb');
    const collections = await db.listCollections().toArray();
    console.log('Collections:', collections.map(c => c.name));

    await client.close();
  } catch (error) {
    console.error('Authentication failed:', error.message);
    console.error('Full error:', error);
  }
}

testAuth();