--- a/inc/Auth/CimdResolver.php
+++ b/inc/Auth/CimdResolver.php
@@ -243,6 +243,11 @@
 
 		// Only public clients are supported (no shared secret to authenticate).
 		$auth_method = isset( $doc['token_endpoint_auth_method'] ) ? (string) $doc['token_endpoint_auth_method'] : 'none';
+		// AdMindra: negotiate the public method supported by both parties (MCP SEP-3149).
+		if ( array_key_exists( 'token_endpoint_auth_methods_supported', $doc ) ) {
+			$methods = $doc['token_endpoint_auth_methods_supported'];
+			$auth_method = is_array( $methods ) && in_array( 'none', $methods, true ) ? 'none' : 'unsupported';
+		}
 		if ( 'none' !== $auth_method ) {
 			McpLogger::log(
 				'CIMD',
--- a/inc/Auth/ClaudeClientVerifier.php
+++ b/inc/Auth/ClaudeClientVerifier.php
@@ -142,6 +142,10 @@
 		// the publisher's CIMD document includes additional redirect URIs for other products.
 		$auth_method = (string) ( $doc['token_endpoint_auth_method'] ?? 'none' );
 
+		// AdMindra: a legacy preference is not binding when plural methods are present.
+		if ( array_key_exists( 'token_endpoint_auth_methods_supported', $doc ) ) {
+			return is_array( $doc['token_endpoint_auth_methods_supported'] ) && in_array( 'none', $doc['token_endpoint_auth_methods_supported'], true );
+		}
 		return 'none' === $auth_method;
 	}
 }
--- a/inc/Auth/JWT.php
+++ b/inc/Auth/JWT.php
@@ -76,7 +76,7 @@
 			return null;
 		}
 
-		if ( $verify_expiry && isset( $payload['exp'] ) && (int) $payload['exp'] < time() ) {
+		if ( $verify_expiry && ( ! isset( $payload['exp'] ) || ! is_numeric( $payload['exp'] ) || (int) $payload['exp'] <= time() || ( isset( $payload['nbf'] ) && (int) $payload['nbf'] > time() ) ) ) {
 			return null;
 		}
 
--- a/inc/Transport/OAuthHttpTransport.php
+++ b/inc/Transport/OAuthHttpTransport.php
@@ -156,6 +156,10 @@
 			return $this->unauthenticated_error( 'invalid_token', 'JWT signature invalid or token expired.' );
 		}
 
+		if ( 'mcp' !== ( $claims['scope'] ?? '' ) || isset( $claims['type'] ) ) {
+			return $this->unauthenticated_error( 'invalid_token', 'Access token with mcp scope required.' );
+		}
+
 		// Audience must match the MCP OAuth REST endpoint.
 		$expected_aud = get_rest_url( null, 'mcp/mcp-oauth-server' );
 		$token_aud    = $claims['aud'] ?? '';
--- a/inc/Auth/TokenEndpoint.php
+++ b/inc/Auth/TokenEndpoint.php
@@ -124,6 +124,12 @@
 			return;
 		}
 
+		// AdMindra: authorization codes are bound to the requesting public client.
+		if ( ! isset( $body['client_id'] ) || ! is_string( $body['client_id'] ) || ! hash_equals( (string) ( $code_data['client_id'] ?? '' ), $body['client_id'] ) ) {
+			$this->send_error( 400, 'invalid_client', 'client_id must match the authorization request.' );
+			return;
+		}
+
 		if ( ! delete_transient( $code_key ) ) {
 			McpLogger::log( 'TOKEN', 'rejected: auth code already consumed (concurrent redemption)' );
 			$this->send_error( 400, 'invalid_grant', 'Code is invalid or has expired.' );
@@ -274,6 +280,12 @@
 				'app_pass_uuid' => $app_pass_uuid,
 			]
 		);
+
+		// AdMindra: refresh tokens remain bound to the original public client.
+		if ( ! isset( $body['client_id'] ) || ! is_string( $body['client_id'] ) || ! hash_equals( $client_id, $body['client_id'] ) ) {
+			$this->send_error( 400, 'invalid_client', 'client_id must match the refresh token.' );
+			return;
+		}
 
 		// Revocation check: if the Application Password was deleted the session is gone.
 		$app_pass = \WP_Application_Passwords::get_user_application_password( $user_id, $app_pass_uuid );