oauth - PHP HMAC-SHA1 function not returning "=" as padding character? -

i trying produce hmac-sha1 signature request access token , token secret tumblr api. using hmac_hash() function in php , understanding algorithm should produce "=" padding @ end of signature, signature returned me function never has padding , think why keep receiving following message tumblr : "oauth_signature not match expected value". have tried using several online signature generators test , produce padding , don't bit confused @ point.

here code:

$params = array(     'oauth_callback' => $callback,     'oauth_consumer_key' => $consumer_key,     'oauth_nonce' => $oauth_nonce,     'oauth_ver' => $oauth_ver,     'oauth_signature_method' => $signature_method,     'oauth_timestamp' => $time                         );  ksort($params);          //--------------- build param string  $params; end($params);    // move internal pointer end of array $lastkey = key($params);  ksort($params);  $param_string; foreach($params $k=>$v) {   $param_string .= rawurlencode(utf8_encode($k))."=".rawurlencode(utf8_encode($v));   if($k != $lastkey) {     $param_string .= "&";             }             };  // --------------- build signature base string $base_string; $base_string .= rawurlencode(utf8_encode($http_method))."&"; $base_string .= rawurlencode(utf8_encode($url))."&"; $base_string .= rawurlencode(utf8_encode($param_string));  //------------------ build signing key $signing_key; $signing_key .= rawurlencode(utf8_encode($consumer_secret))."&";  //------------------ build signature  $signature; $signature = hash_hmac("sha1", $base_string, $signing_key); 

i needed change this: $signature = hash_hmac("sha1", $base_string, $signing_key);

to this: $signature = base64_encode(hash_hmac("sha1", $base_string, $signing_key, true));