[ADDED] UserInfoHandler for dynamically setting user/password

.github/workflows/ci.yaml

@@ -35,7 +35,7 @@ jobs:
 
         strategy:
             matrix:
-              go: [ "1.21", "1.22" ]
+              go: [ "1.22", "1.23" ]
         steps:
             - name: Checkout code
               uses: actions/checkout@v4
@@ -55,14 +55,14 @@ jobs:
               shell: bash --noprofile --norc -x -eo pipefail {0}
               run: |
                 go test -modfile=go_test.mod -v -run=TestNoRace -p=1 ./... --failfast -vet=off
-                if [ "${{ matrix.go }}" = "1.22" ]; then
+                if [ "${{ matrix.go }}" = "1.23" ]; then
                   ./scripts/cov.sh CI
                 else
                   go test -modfile=go_test.mod -race -v -p=1 ./... --failfast -vet=off -tags=internal_testing
                 fi
 
             - name: Coveralls
-              if: matrix.go == '1.22'
+              if: matrix.go == '1.23'
               uses: coverallsapp/github-action@v2
               with:
                file: acc.out

nats.go

@@ -131,6 +131,7 @@ var (
 	ErrNkeysNotSupported           = errors.New("nats: nkeys not supported by the server")
 	ErrStaleConnection             = errors.New("nats: " + STALE_CONNECTION)
 	ErrTokenAlreadySet             = errors.New("nats: token and token handler both set")
+	ErrUserInfoAlreadySet          = errors.New("nats: cannot set user info callback and user/pass")
 	ErrMsgNotBound                 = errors.New("nats: message is not bound to subscription/connection")
 	ErrMsgNoReply                  = errors.New("nats: message does not have a reply")
 	ErrClientIPNotSupported        = errors.New("nats: client IP not supported by this server")
@@ -230,6 +231,9 @@ type SignatureHandler func([]byte) ([]byte, error)
 // AuthTokenHandler is used to generate a new token.
 type AuthTokenHandler func() string
 
+// UserInfoCB is used to pass the username and password when establishing connection.
+type UserInfoCB func() (string, string)
+
 // ReconnectDelayHandler is used to get from the user the desired
 // delay the library should pause before attempting to reconnect
 // again. Note that this is invoked after the library tried the
@@ -443,6 +447,9 @@ type Options struct {
 	// Password sets the password to be used when connecting to a server.
 	Password string
 
+	// UserInfo sets the callback handler that will fetch the username and password.
+	UserInfo UserInfoCB
+
 	// Token sets the token to be used when connecting to a server.
 	Token string
 
@@ -1166,6 +1173,13 @@ func UserInfo(user, password string) Option {
 	}
 }
 
+func UserInfoHandler(cb UserInfoCB) Option {
+	return func(o *Options) error {
+		o.UserInfo = cb
+		return nil
+	}
+}
+
 // Token is an Option to set the token to use
 // when a token is not included directly in the URLs
 // and when a token handler is not provided.
@@ -2563,6 +2577,13 @@ func (nc *Conn) connectProto() (string, error) {
 		pass = o.Password
 		token = o.Token
 		nkey = o.Nkey
+
+		if nc.Opts.UserInfo != nil {
+			if user != _EMPTY_ || pass != _EMPTY_ {
+				return _EMPTY_, ErrUserInfoAlreadySet
+			}
+			user, pass = nc.Opts.UserInfo()
+		}
 	}
 
 	// Look for user jwt.

test/auth_test.go

@@ -17,6 +17,8 @@ import (
 	"errors"
 	"fmt"
 	"io/fs"
+	"net"
+	"os"
 	"strings"
 	"sync/atomic"
 	"testing"
@@ -377,3 +379,75 @@ func TestConnectMissingCreds(t *testing.T) {
 		t.Fatalf("Expected not exists error, got: %v", err)
 	}
 }
+
+func TestUserInfoHandler(t *testing.T) {
+	conf := createConfFile(t, []byte(`
+	listen: 127.0.0.1:-1
+	accounts: {
+	  A {
+		users: [{ user: "pp", password: "foo" }]
+	  }
+	}
+`))
+	defer os.Remove(conf)
+
+	s, _ := RunServerWithConfig(conf)
+	defer s.Shutdown()
+
+	user, pass := "pp", "foo"
+	userInfoCB := func() (string, string) {
+		return user, pass
+	}
+
+	// check that we cannot set the user info twice
+	_, err := nats.Connect(s.ClientURL(), nats.UserInfo("pp", "foo"), nats.UserInfoHandler(userInfoCB))
+	if !errors.Is(err, nats.ErrUserInfoAlreadySet) {
+		t.Fatalf("Expected ErrUserInfoAlreadySet, got: %v", err)
+	}
+
+	addr, ok := s.Addr().(*net.TCPAddr)
+	if !ok {
+		t.Fatalf("Expected a TCP address, got %T", addr)
+	}
+
+	// check that user/pass from url takes precedence
+	_, err = nats.Connect(fmt.Sprintf("nats://bad:bad@localhost:%d", addr.Port),
+		nats.UserInfoHandler(userInfoCB))
+	if !errors.Is(err, nats.ErrAuthorization) {
+		t.Fatalf("Expected ErrAuthorization, got: %v", err)
+	}
+
+	// connect using the handler
+	nc, err := nats.Connect(s.ClientURL(),
+		nats.ReconnectWait(100*time.Millisecond),
+		nats.UserInfoHandler(userInfoCB))
+	if err != nil {
+		t.Fatalf("Error on connect: %v", err)
+	}
+	defer nc.Close()
+
+	// now change the password and reload the server
+	newConfig := []byte(`
+	listen: 127.0.0.1:-1
+	accounts: {
+	  A {
+		users: [{ user: "dd", password: "bar" }]
+	  }
+	}
+`)
+	if err := os.WriteFile(conf, newConfig, 0666); err != nil {
+		t.Fatalf("Error writing conf file: %v", err)
+	}
+
+	// update the user info used by the callback
+	user, pass = "dd", "bar"
+
+	status := nc.StatusChanged(nats.CONNECTED)
+
+	if err := s.Reload(); err != nil {
+		t.Fatalf("Error on reload: %v", err)
+	}
+
+	// we should get a reconnected event meaning the new credentials were used
+	WaitOnChannel(t, status, nats.CONNECTED)
+}