Attempting to access a Solr core URI through a browser, will result in a 404 Not Found response code.
Please note that this is expected behavior. In addition to securing Solr operations using HMAC authentication, Acquia also displays 404 errors when no proper authentication is being used (e.g. when visiting these links from a browser). However, some URLs are available, such as: https://useast1-c26.acquia-search.com/solr/GHRV-134033/admin/ping
Accessing the page above reflects an OK status response:
<response> <lst name="responseHeader">...</lst> <str name="status">OK</str> </response>