Authenticating with a User and Password

For this example, start the server using:
nats-server --user myname --pass password
You can encrypt passwords to pass to 
nats-server using the simple NATS CLI tool:
nats server passwd
? Enter password [? for help] **********************
? Reenter password [? for help] **********************
$2a$11$qbtrnb0mSG2eV55xoyPqHOZx/lLBlryHRhU3LK2oOPFRwGF/5rtGK
and use the hashed password in the server config. The client still uses the plain text version.
The code uses localhost:4222 so that you can start the server on your machine to try them out.
Connecting with a User/Password
When logging in with a password 
nats-server will take either a plain text password or an encrypted password.
Go
// Set a user and plain text password
nc, err := nats.Connect("127.0.0.1", nats.UserInfo("myname", "password"))
if err != nil {
    log.Fatal(err)
}
defer nc.Close()
// Do something with the connection
Java
Options options = new Options.Builder()
    .server("nats://localhost:4222")
    .userInfo("myname","password") // Set a user and plain text password
    .build();
Connection nc = Nats.connect(options);
// Do something with the connection
nc.close();
JavaScript
 const nc = await connect({
      port: ns.port,
      user: "byname",
      pass: "password",
});
Python
nc = NATS()
await nc.connect(servers=["nats://myname:password@demo.nats.io:4222"])
# Do something with the connection.
C#
// dotnet add package NATS.Net
using NATS.Net;
using NATS.Client.Core;
await using var client = new NatsClient(new NatsOpts
{
    Url = "nats://localhost:4222",
    AuthOpts = new NatsAuthOpts
    {
        Username = "myname",
        Password = "password",
    }
});
Ruby
require 'nats/client'
NATS.start(servers:["nats://myname:password@127.0.0.1:4222"], name: "my-connection") do |nc|
   nc.on_error do |e|
    puts "Error: #{e}"
  end
   nc.on_reconnect do
    puts "Got reconnected to #{nc.connected_server}"
  end
  nc.on_disconnect do |reason|
    puts "Got disconnected! #{reason}"
  end
  nc.close
end
C
natsConnection      *conn      = NULL;
natsOptions         *opts      = NULL;
natsStatus          s          = NATS_OK;
s = natsOptions_Create(&opts);
if (s == NATS_OK)
    s = natsOptions_SetUserInfo(opts, "myname", "password");
if (s == NATS_OK)
    s = natsConnection_Connect(&conn, opts);
(...)
// Destroy objects that were created
natsConnection_Destroy(conn);
natsOptions_Destroy(opts);
Connecting with a User/Password in the URL
Most clients make it easy to pass the user name and password by accepting them in the URL for the server. This standard format is:
nats://user:password@server:port
Using this format, you can connect to a server using authentication as easily as you connected with a URL:
Go
// Set a user and plain text password
nc, err := nats.Connect("myname:password@127.0.0.1")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()
// Do something with the connection
Java
Connection nc = Nats.connect("nats://myname:password@localhost:4222");
// Do something with the connection
nc.close();
JavaScript
// JavaScript clients don't support username/password in urls use `user` and `pass` options.
Python
nc = NATS()
await nc.connect(servers=["nats://myname:password@demo.nats.io:4222"])
# Do something with the connection.
C#
// dotnet add package NATS.Net
using NATS.Net;
using NATS.Client.Core;
await using var nc = new NatsClient(new NatsOpts
{
    // .NET client doesn't support username/password in URLs
    // use `Username` and `Password` options.
    Url = "nats://demo.nats.io:4222",
    AuthOpts = new NatsAuthOpts
    {
        Username = "myname",
        Password = "password",
    }
});
Ruby
require 'nats/client'
NATS.start(servers:["nats://myname:password@127.0.0.1:4222"], name: "my-connection") do |nc|
   nc.on_error do |e|
    puts "Error: #{e}"
  end
   nc.on_reconnect do
    puts "Got reconnected to #{nc.connected_server}"
  end
  nc.on_disconnect do |reason|
    puts "Got disconnected! #{reason}"
  end
  nc.close
end
C
natsConnection      *conn      = NULL;
natsOptions         *opts      = NULL;
natsStatus          s          = NATS_OK;
s = natsOptions_Create(&opts);
if (s == NATS_OK)
    s = natsOptions_SetURL(opts, "nats://myname:password@127.0.0.1:4222");
if (s == NATS_OK)
    s = natsConnection_Connect(&conn, opts);
(...)
// Destroy objects that were created
natsConnection_Destroy(conn);
natsOptions_Destroy(opts);