Magento 2 – Resolving Customer/Token Rest API Issues

Right now you are able to access only that api which can be accessed anonymously. Now you are accessing a api which need a authentication key/access token to assure that you are a registered customer who is accessing such api's. So for generating you have to generate a access token using below api :

{base_url}/rest/V1/integration/customer/token

this is a post type api, so you have to pass the username and password in the body,

{
"username":"{your_username}",
"password":"{password}"
}

and hit it, you will get a access token like this :

"6fomgh65em5jaivxqllorc50h2gqrhhe"

Now you have to use this access token in the api you are currently trying to access : In Postman -> go to header and in key = Authorization and in value = Bearer {your generated token} and hit SEND

DONE, That's All.

webapi.xml

<route url="/V1/test/most/" method="GET">
  <service class="Vendor\Module\Api\TestRepositoryInterface" method="getTest"/>
  <resources>
      <resource ref="self"/>
  </resources>
        <data>
            <parameter name="customerId" force="true">%customer_id%</parameter>
        </data>
 </route>

in this API call you'll get customer ID and based on ID you can get Customer data.

Another solution

$ch = curl_init('dev.magento2.com/rest/V1/customers/me');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: application/json'
));
curl_setopt($ch, CURLOPT_COOKIE, 'PHPSESSID=' . $_COOKIE['PHPSESSID']);
curl_setopt($ch, CURLOPT_TIMEOUT, 5);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);

//execute post
$result = curl_exec($ch);

//close connection
curl_close($ch);

$json = json_decode($result);
echo $json->id;