Example API call snippets using tokens and transients

api.php

private function api_call( $url ) {
// a transient is used to store the token, this token in this API expires in 60 minute
		if ( false === ( $this->api_token = get_transient( 'my_api_token' ) ) ) {
			$response      = $this->api_get_token( $url );
			$response_code = wp_remote_retrieve_response_code( $response );
		} else {
			$args     = array(
				'headers' => array(
					'Authorization' => 'Basic ' . $this->api_token,
				),
				'timeout' => 25,
			);
			$response = wp_remote_get( $url, $args );
			if ( is_wp_error( $response ) ) {
				die( sprintf( esc_html__( 'Failed getting %1$s %2$s', 'fullworks' ), $url, print_r( $response, true ) ) );
			}
			$response_code = wp_remote_retrieve_response_code( $response );
			if ( $response_code == 401 ) {
				// token not valid
				$response = $this->api_get_token( $url );
			}
		}
		$body = wp_remote_retrieve_body( $response );

// this api returns xml response

		return array(
			'response_code' => $response_code,
			'body'          => simplexml_load_string( $body ),
		);
	}

private function api_get_token( $url ) {
	// called if basic auth not worked
    	// user name and apsswords stored in settings
	$args     = array(
			'headers' => array(
				'Authorization' => 'Basic ' . base64_encode( $this->get_setting( 'api', 'username' ) . ':' . $this->get_setting( 'api', 'password' ) )
			),
			'timeout' => 25,
		);
		$response = wp_remote_get( $url, $args );
		if ( is_wp_error( $response ) ) {
			die( sprintf( esc_html__( 'Failed getting %1$s %2$s', 'fullworks' ), $url, print_r( $response, true ) ) );
		}
		$response_code = wp_remote_retrieve_response_code( $response );
		if ( ( $response_code != 200 ) && ( $response_code != 304 ) ) {
			die( sprintf( esc_html__( 'Failed getting %1$s with code %2$s', 'fullworks' ), $url, print_r( $response_code, true ) ) );
		}
		// could add check for 401 and sleep 10 minutes  if this becomes a problem.
		$this->api_token = base64_encode( wp_remote_retrieve_header( $response, 'Token' ) );
		set_transient( 'my_api_token', $this->api_token, HOUR_IN_SECONDS );

		return $response;
}