Cannot access the plugin repository

I cannot install plugins any more. It worked before.

As far as I know Grafana gets its plugins from

If I try to access that, I get an HTTP 403 error:

# curl

<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>403 Forbidden</title>
<body text=#000000 bgcolor=#ffffff>
<h1>Error: Forbidden</h1>
<h2>Your client does not have permission to get URL <code>/api/plugins</code> from this server.</h2>