diff --git a/internal/resource/configmap.go b/internal/resource/configmap.go
index b05e2d832..710e7f5dd 100644
--- a/internal/resource/configmap.go
+++ b/internal/resource/configmap.go
@@ -101,6 +101,26 @@ func (builder *ServerConfigMapBuilder) Update(object client.Object) error {
 		return err
 	}
 
+	rmqProperties := builder.Instance.Spec.Rabbitmq
+	authMechsConfigured, err := areAuthMechanismsConfigued(rmqProperties.AdditionalConfig)
+	if err != nil {
+		return err
+	}
+	// By default, RabbitMQ configures the following SASL mechanisms:
+	// auth_mechanisms.1 = PLAIN
+	// auth_mechanisms.2 = AMQPLAIN
+	// auth_mechanisms.3 = ANONYMOUS
+	if !authMechsConfigured {
+		// Since the user didn't explicitly configure auth mechanisms, we disable
+		// ANONYMOUS logins because they should be disabled in production.
+		if _, err := defaultSection.NewKey("auth_mechanisms.1", "PLAIN"); err != nil {
+			return err
+		}
+		if _, err := defaultSection.NewKey("auth_mechanisms.2", "AMQPLAIN"); err != nil {
+			return err
+		}
+	}
+
 	userConfiguration := ini.Empty()
 	userConfigurationSection := userConfiguration.Section("")
 
@@ -231,7 +251,6 @@ func (builder *ServerConfigMapBuilder) Update(object client.Object) error {
 
 	rmqConfBuffer.Reset()
 
-	rmqProperties := builder.Instance.Spec.Rabbitmq
 	if err := userConfiguration.Append([]byte(rmqProperties.AdditionalConfig)); err != nil {
 		return fmt.Errorf("failed to append spec.rabbitmq.additionalConfig: %w", err)
 	}
@@ -307,3 +326,18 @@ func removeHeadroom(memLimit int64) int64 {
 	}
 	return memLimit - memLimit/5
 }
+
+func areAuthMechanismsConfigued(additionalConfig string) (bool, error) {
+	iniFile, err := ini.Load([]byte(additionalConfig))
+	if err != nil {
+		return false, fmt.Errorf("failed to load spec.rabbitmq.additionalConfig: %w", err)
+	}
+
+	section := iniFile.Section("")
+	for _, key := range section.KeyStrings() {
+		if strings.HasPrefix(key, "auth_mechanisms") {
+			return true, nil
+		}
+	}
+	return false, nil
+}
diff --git a/internal/resource/configmap_test.go b/internal/resource/configmap_test.go
index fb537f1f1..dffc2edec 100644
--- a/internal/resource/configmap_test.go
+++ b/internal/resource/configmap_test.go
@@ -36,7 +36,10 @@ cluster_formation.peer_discovery_backend   = rabbit_peer_discovery_k8s
 cluster_formation.k8s.host                 = kubernetes.default
 cluster_formation.k8s.address_type         = hostname
 cluster_formation.target_cluster_size_hint = 1
-cluster_name                               = ` + instanceName)
+cluster_name                               = ` + instanceName + `
+auth_mechanisms.1                          = PLAIN
+auth_mechanisms.2                          = AMQPLAIN
+`)
 }
 
 var _ = Describe("GenerateServerConfigMap", func() {
@@ -168,6 +171,22 @@ var _ = Describe("GenerateServerConfigMap", func() {
 				Expect(configMapBuilder.Update(configMap)).To(Succeed())
 				Expect(configMap.Data).To(HaveKeyWithValue("userDefinedConfiguration.conf", expectedConfiguration))
 			})
+
+			When("user restricts SSL mechanisms to EXTERNAL", func() {
+				It("adds only EXTERNAL", func() {
+					userDefinedConfiguration := "auth_mechanisms.1 = EXTERNAL"
+					instance.Spec.Rabbitmq.AdditionalConfig = userDefinedConfiguration
+					expectedConfiguration := iniString(userDefinedConfiguration)
+
+					Expect(configMapBuilder.Update(configMap)).To(Succeed())
+					Expect(configMap.Data).To(HaveKeyWithValue("userDefinedConfiguration.conf", expectedConfiguration))
+					Expect(configMap.Data).To(HaveKey("operatorDefaults.conf"))
+					operatorDefaults := configMap.Data["operatorDefaults.conf"]
+					Expect(operatorDefaults).NotTo(ContainSubstring("auth_mechanisms"))
+					Expect(operatorDefaults).NotTo(ContainSubstring("PLAIN"))
+					Expect(operatorDefaults).NotTo(ContainSubstring("ANONYMOUS"))
+				})
+			})
 		})
 
 		When("invalid userDefinedConfiguration is provided", func() {