When you look at
webapi.xml you could see route of above mentioned api defined like this:
<route url="/V1/products" method="GET"> <service class="Magento\Catalog\Api\ProductRepositoryInterface" method="save"/> <resources> <resource ref="Magento_Catalog::products" /> </resources> </route>
ref="Magento_Catalog::products" means that only users with configured ACL which allow access to this resource are allowed to get it. In magento ONLY admin user can have a configuration of ACL.
So that you will have to use
admin token or
Get an admin token :
Method:POST Endpoint: /V1/integration/admin/token
For More details refer this official documentation : https://devdocs.magento.com/guides/v2.3/get-started/authentication/gs-authentication-token.html
You need to pass Admin token in Headers. Below is docs to get Admin token in Maganto 2.