There are many other corner cases, but here are some of the most common authentication responses from Solr.
If Authorization is configured in Solr, and a call is rejected by authorization, then a HTTP 403 response is returned
HTTP/2 401
content-security-policy: default-src 'none'; base-uri 'none'; connect-src 'self'; form-action 'self'; font-src 'self'; frame-ancestors 'none'; img-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'self'; worker-src 'self';
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
www-authenticate: Bearer realm="solr-jwt", error="invalid_token", error_description="JWT token expired"
x-solr-authdata: ewogICJzY29wZSI6InNvbHIiLAogICJyZWRpcmVjdF91cmlzIjpbImh0dHBzOi8vc29scjo4OTgzL3NvbHIvIl0sCiAgImF1dGhvcml6YXRpb25FbmRwb2ludCI6Imh0dHBzOi8vaWRwOjgwODEvYzJpZC1sb2dpbi8iLAogICJjbGllbnRfaWQiOiJ0eXJyaWV6dXBmN3JhIn0=
cache-control: must-revalidate,no-cache,no-store
content-type: text/html;charset=iso-8859-1
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<title>Error 401 JWT token expired</title>
</head>
<body><h2>HTTP ERROR 401 JWT token expired</h2>
<table>
<tr><th>URI:</th><td>/solr/admin/info/health</td></tr>
<tr><th>STATUS:</th><td>401</td></tr>
<tr><th>MESSAGE:</th><td>JWT token expired</td></tr>
<tr><th>SERVLET:</th><td>default</td></tr>
</table>
</body>
</html>
HTTP/2 401
content-security-policy: default-src 'none'; base-uri 'none'; connect-src 'self'; form-action 'self'; font-src 'self'; frame-ancestors 'none'; img-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'self'; worker-src 'self';
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
www-authenticate: Bearer realm="solr-jwt"
x-solr-authdata: ewogICJzY29wZSI6InNvbHIiLAogICJyZWRpcmVjdF91cmlzIjpbImh0dHBzOi8vc29scjo4OTgzL3NvbHIvIl0sCiAgImF1dGhvcml6YXRpb25FbmRwb2ludCI6Imh0dHBzOi8vaWRwOjgwODEvYzJpZC1sb2dpbi8iLAogICJjbGllbnRfaWQiOiJ0eXJyaWV6dXBmN3JhIn0=
cache-control: must-revalidate,no-cache,no-store
content-type: text/html;charset=iso-8859-1
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<title>Error 401 Require authentication</title>
</head>
<body><h2>HTTP ERROR 401 Require authentication</h2>
<table>
<tr><th>URI:</th><td>/solr/admin/info/health</td></tr>
<tr><th>STATUS:</th><td>401</td></tr>
<tr><th>MESSAGE:</th><td>Require authentication</td></tr>
<tr><th>SERVLET:</th><td>default</td></tr>
</table>
</body>
</html>
HTTP/2 400
content-security-policy: default-src 'none'; base-uri 'none'; connect-src 'self'; form-action 'self'; font-src 'self'; frame-ancestors 'none'; img-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'self'; worker-src 'self';
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
www-authenticate: Bearer realm="solr-jwt", error="invalid_request", error_description="Invalid JWT"
x-solr-authdata: ewogICJzY29wZSI6InNvbHIiLAogICJyZWRpcmVjdF91cmlzIjpbImh0dHBzOi8vc29scjo4OTgzL3NvbHIvIl0sCiAgImF1dGhvcml6YXRpb25FbmRwb2ludCI6Imh0dHBzOi8vaWRwOjgwODEvYzJpZC1sb2dpbi8iLAogICJjbGllbnRfaWQiOiJ0eXJyaWV6dXBmN3JhIn0=
cache-control: must-revalidate,no-cache,no-store
content-type: text/html;charset=iso-8859-1
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<title>Error 400 Invalid JWT</title>
</head>
<body><h2>HTTP ERROR 400 Invalid JWT</h2>
<table>
<tr><th>URI:</th><td>/solr/admin/info/health</td></tr>
<tr><th>STATUS:</th><td>400</td></tr>
<tr><th>MESSAGE:</th><td>Invalid JWT</td></tr>
<tr><th>SERVLET:</th><td>default</td></tr>
</table>
</body>
</html>
HTTP/2 401
content-security-policy: default-src 'none'; base-uri 'none'; connect-src 'self'; form-action 'self'; font-src 'self'; frame-ancestors 'none'; img-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'self'; worker-src 'self';
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
www-authenticate: Bearer realm="solr-jwt", error="invalid_token", error_description="JWT validation failed"
x-solr-authdata: ewogICJzY29wZSI6InNvbHIiLAogICJyZWRpcmVjdF91cmlzIjpbImh0dHBzOi8vc29scjo4OTgzL3NvbHIvIl0sCiAgImF1dGhvcml6YXRpb25FbmRwb2ludCI6Imh0dHBzOi8vaWRwOjgwODEvYzJpZC1sb2dpbi8iLAogICJjbGllbnRfaWQiOiJ0eXJyaWV6dXBmN3JhIn0=
cache-control: must-revalidate,no-cache,no-store
content-type: text/html;charset=iso-8859-1
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<title>Error 401 JWT validation failed</title>
</head>
<body><h2>HTTP ERROR 401 JWT validation failed</h2>
<table>
<tr><th>URI:</th><td>/solr/admin/info/health</td></tr>
<tr><th>STATUS:</th><td>401</td></tr>
<tr><th>MESSAGE:</th><td>JWT validation failed</td></tr>
<tr><th>SERVLET:</th><td>default</td></tr>
</table>
</body>
</html>