Add support for OAuth

Support for OAuth authentication got introduced in Postgres 18.

Author: dvob

conn.go

@@ -9,6 +9,7 @@ import (
 	"database/sql"
 	"database/sql/driver"
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -1143,6 +1144,10 @@ func isDriverSetting(key string) bool {
 		return true
 	case "password":
 		return true
+	case "oauth_token":
+		return true
+	case "oauth_token_file":
+		return true
 	case "sslmode", "sslcert", "sslkey", "sslrootcert", "sslinline", "sslsni":
 		return true
 	case "fallback_application_name":
@@ -1290,59 +1295,135 @@ func (cn *conn) auth(r *readBuf, o values) {
 		// from the server..
 
 	case 10:
-		sc := scram.NewClient(sha256.New, o["user"], o["password"])
-		sc.Step(nil)
-		if sc.Err() != nil {
-			errorf("SCRAM-SHA-256 error: %s", sc.Err().Error())
+		switch saslMethod := r.string(); saslMethod {
+		case "SCRAM-SHA-256":
+			cn.saslScram(o)
+		case "OAUTHBEARER":
+			cn.saslOAuth(o)
 		}
-		scOut := sc.Out()
 
-		w := cn.writeBuf('p')
-		w.string("SCRAM-SHA-256")
-		w.int32(len(scOut))
-		w.bytes(scOut)
-		cn.send(w)
+	default:
+		errorf("unknown authentication response: %d", code)
+	}
+}
 
-		t, r := cn.recv()
-		if t != 'R' {
-			errorf("unexpected password response: %q", t)
-		}
+func (cn *conn) saslScram(o values) {
+	sc := scram.NewClient(sha256.New, o["user"], o["password"])
+	sc.Step(nil)
+	if sc.Err() != nil {
+		errorf("SCRAM-SHA-256 error: %s", sc.Err().Error())
+	}
+	scOut := sc.Out()
 
-		if r.int32() != 11 {
-			errorf("unexpected authentication response: %q", t)
-		}
+	w := cn.writeBuf('p')
+	w.string("SCRAM-SHA-256")
+	w.int32(len(scOut))
+	w.bytes(scOut)
+	cn.send(w)
 
-		nextStep := r.next(len(*r))
-		sc.Step(nextStep)
-		if sc.Err() != nil {
-			errorf("SCRAM-SHA-256 error: %s", sc.Err().Error())
-		}
+	t, r := cn.recv()
+	if t != 'R' {
+		errorf("unexpected password response: %q", t)
+	}
 
-		scOut = sc.Out()
-		w = cn.writeBuf('p')
-		w.bytes(scOut)
-		cn.send(w)
+	if r.int32() != 11 {
+		errorf("unexpected authentication response: %q", t)
+	}
 
-		t, r = cn.recv()
-		if t != 'R' {
-			errorf("unexpected password response: %q", t)
-		}
+	nextStep := r.next(len(*r))
+	sc.Step(nextStep)
+	if sc.Err() != nil {
+		errorf("SCRAM-SHA-256 error: %s", sc.Err().Error())
+	}
 
-		if r.int32() != 12 {
-			errorf("unexpected authentication response: %q", t)
+	scOut = sc.Out()
+	w = cn.writeBuf('p')
+	w.bytes(scOut)
+	cn.send(w)
+
+	t, r = cn.recv()
+	if t != 'R' {
+		errorf("unexpected password response: %q", t)
+	}
+
+	if r.int32() != 12 {
+		errorf("unexpected authentication response: %q", t)
+	}
+
+	nextStep = r.next(len(*r))
+	sc.Step(nextStep)
+	if sc.Err() != nil {
+		errorf("SCRAM-SHA-256 error: %s", sc.Err().Error())
+	}
+}
+
+func (cn *conn) saslOAuth(o values) {
+	// https://www.rfc-editor.org/rfc/rfc7628.html#section-3.1
+	w := cn.writeBuf('p')
+	w.string("OAUTHBEARER")
+
+	token, err := getOAuthToken(o)
+	if err != nil {
+		errorf("failed to obtain oauth token: %s", err)
+	}
+	initialResponse := []byte("n,,\x01auth=Bearer " + token + "\x01\x01")
+	w.int32(len(initialResponse))
+	w.bytes(initialResponse)
+	cn.send(w)
+
+	t, r := cn.recv()
+	if t != 'R' {
+		errorf("unexpected oauth response: %q", t)
+	}
+
+	if code := r.int32(); code != 0 {
+		// usually on an authentication error we should get a
+		// AuthenticationSASLContinue message
+		if code != 11 {
+			errorf("unexpected oauth response: %q %d", t, code)
 		}
 
-		nextStep = r.next(len(*r))
-		sc.Step(nextStep)
-		if sc.Err() != nil {
-			errorf("SCRAM-SHA-256 error: %s", sc.Err().Error())
+		// the AuthenticationSASLContinue does have an error payload
+		// https://www.rfc-editor.org/rfc/rfc7628.html#section-3.2.2
+		errResponse := struct {
+			Status              string `json:"status"`
+			Scope               string `json:"scope"`
+			OpenIDConfiguration string `json:"openid-configuration"`
+		}{}
+		err := json.Unmarshal(*r, &errResponse)
+		if err != nil {
+			errorf("invalid oauth error response")
 		}
 
-	default:
-		errorf("unknown authentication response: %d", code)
+		errorf("oauth authentication failed '%s'", errResponse.Status)
+
+		// https://www.rfc-editor.org/rfc/rfc7628.html#section-3.2.3
+		// we deliberately don't complete the error messaging sequence as described
+		// in 3.2.3 as we're going to close the connection either way
+		// w = cn.writeBuf('p')
+		// w.int32(1)
+		// w.bytes([]byte{0x01})
+		// cn.send(w)
 	}
 }
 
+func getOAuthToken(o values) (string, error) {
+	if token, ok := o["oauth_token"]; ok {
+		return token, nil
+	}
+
+	if tokenFile, ok := o["oauth_token_file"]; ok {
+		rawToken, err := os.ReadFile(tokenFile)
+		if err != nil {
+			return "", err
+		}
+		rawToken = bytes.TrimSuffix(rawToken, []byte("\n"))
+		return string(rawToken), nil
+	}
+
+	return "", fmt.Errorf("no oauth token configured")
+}
+
 type format int
 
 const formatText format = 0