add LDAP StartTLS support (#9472)

cmd/config/identity/ldap/config.go

@@ -58,6 +58,7 @@ type Config struct {
 	stsExpiryDuration time.Duration // contains converted value
 	tlsSkipVerify     bool          // allows skipping TLS verification
 	serverInsecure    bool          // allows plain text connection to LDAP Server
+	serverStartTLS    bool          // allows plain text connection to LDAP Server
 	rootCAs           *x509.CertPool
 }
 
@@ -73,11 +74,13 @@ const (
 	GroupSearchBaseDN    = "group_search_base_dn"
 	TLSSkipVerify        = "tls_skip_verify"
 	ServerInsecure       = "server_insecure"
+	ServerStartTLS       = "server_starttls"
 
 	EnvServerAddr           = "MINIO_IDENTITY_LDAP_SERVER_ADDR"
 	EnvSTSExpiry            = "MINIO_IDENTITY_LDAP_STS_EXPIRY"
 	EnvTLSSkipVerify        = "MINIO_IDENTITY_LDAP_TLS_SKIP_VERIFY"
 	EnvServerInsecure       = "MINIO_IDENTITY_LDAP_SERVER_INSECURE"
+	EnvServerStartTLS       = "MINIO_IDENTITY_LDAP_SERVER_STARTTLS"
 	EnvUsernameFormat       = "MINIO_IDENTITY_LDAP_USERNAME_FORMAT"
 	EnvUsernameSearchFilter = "MINIO_IDENTITY_LDAP_USERNAME_SEARCH_FILTER"
 	EnvUsernameSearchBaseDN = "MINIO_IDENTITY_LDAP_USERNAME_SEARCH_BASE_DN"
@@ -129,6 +132,10 @@ var (
 			Key:   ServerInsecure,
 			Value: config.EnableOff,
 		},
+		config.KV{
+			Key:   ServerStartTLS,
+			Value: config.EnableOff,
+		},
 	}
 )
 
@@ -257,6 +264,18 @@ func (l *Config) Connect() (ldapConn *ldap.Conn, err error) {
 		return ldap.Dial("tcp", l.ServerAddr)
 	}
 
+	if l.serverStartTLS {
+		conn, err := ldap.Dial("tcp", l.ServerAddr)
+		if err != nil {
+			return nil, err
+		}
+		err = conn.StartTLS(&tls.Config{
+			InsecureSkipVerify: l.tlsSkipVerify,
+			RootCAs:            l.rootCAs,
+		})
+		return conn, err
+	}
+
 	return ldap.DialTLS("tcp", l.ServerAddr, &tls.Config{
 		InsecureSkipVerify: l.tlsSkipVerify,
 		RootCAs:            l.rootCAs,
@@ -303,6 +322,12 @@ func Lookup(kvs config.KVS, rootCAs *x509.CertPool) (l Config, err error) {
 			return l, err
 		}
 	}
+	if v := env.Get(EnvServerStartTLS, kvs.Get(ServerStartTLS)); v != "" {
+		l.serverStartTLS, err = config.ParseBool(v)
+		if err != nil {
+			return l, err
+		}
+	}
 	if v := env.Get(EnvTLSSkipVerify, kvs.Get(TLSSkipVerify)); v != "" {
 		l.tlsSkipVerify, err = config.ParseBool(v)
 		if err != nil {

docs/sts/ldap.md

@@ -38,7 +38,7 @@ LDAP configuration is designed to be simple for the MinIO administrator. The ful
 
 MinIO can be configured to find the groups of a user from AD/LDAP by specifying the **MINIO_IDENTITY_LDAP_GROUP_SEARCH_FILTER** and **MINIO_IDENTITY_LDAP_GROUP_NAME_ATTRIBUTE** environment variables. When a user logs in via the STS API, the MinIO server queries the AD/LDAP server with the given search filter and extracts the given attribute from the search results. These values represent the groups that the user is a member of. On each access MinIO applies the IAM policies attached to these groups in MinIO.
 
-MinIO sends LDAP credentials to LDAP server for validation. So we _strongly recommend_ to use MinIO with AD/LDAP server over TLS _only_. Using plain-text connection between MinIO and LDAP server means _credentials can be compromised_ by anyone listening to network traffic.
+MinIO sends LDAP credentials to LDAP server for validation. So we _strongly recommend_ to use MinIO with AD/LDAP server over TLS or StartTLS _only_. Using plain-text connection between MinIO and LDAP server means _credentials can be compromised_ by anyone listening to network traffic.
 
 LDAP is configured via the following environment variables:
 
@@ -57,11 +57,12 @@ MINIO_IDENTITY_LDAP_USERNAME_SEARCH_BASE_DN  (list)      ";" separated list of u
 MINIO_IDENTITY_LDAP_GROUP_NAME_ATTRIBUTE     (string)    search attribute for group name e.g. "cn"
 MINIO_IDENTITY_LDAP_STS_EXPIRY               (duration)  temporary credentials validity duration in s,m,h,d. Default is "1h"
 MINIO_IDENTITY_LDAP_TLS_SKIP_VERIFY          (on|off)    trust server TLS without verification, defaults to "off" (verify)
+MINIO_IDENTITY_LDAP_SERVER_STARTTLS          (on|off)    use StartTLS instead of TLS
 MINIO_IDENTITY_LDAP_SERVER_INSECURE          (on|off)    allow plain text connection to AD/LDAP server, defaults to "off"
 MINIO_IDENTITY_LDAP_COMMENT                  (sentence)  optionally add a comment to this setting
 ```
 
-MinIO sends LDAP credentials to LDAP server for validation. So we _strongly recommend_ to use MinIO with AD/LDAP server over TLS _only_. Using plain-text connection between MinIO and LDAP server means _credentials can be compromised_ by anyone listening to network traffic.
+MinIO sends LDAP credentials to LDAP server for validation. So we _strongly recommend_ to use MinIO with AD/LDAP server over TLS or StartTLS _only_. Using plain-text connection between MinIO and LDAP server means _credentials can be compromised_ by anyone listening to network traffic.
 
 If a self-signed certificate is being used, the certificate can be added to MinIO's certificates directory, so it can be trusted by the server. An example setup for development or experimentation: