...
In summary, use the plugin command that ships with the IdP to install the plugin from either a local file pre-downloaded, or from a URL.
Installation
...
$
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/opt/shibboleth-idp/bin/plugin.sh
...
-i
...
<plugin.tar.gz>
...
or
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C:>\opt\shibboleth-idp\bin\plugin.bat
...
-i
...
<plugin.zip>
If installing from a local file, you need to ensure the GPG detached signature (e.g. the .asc file) is placed alongside the main plugin archive on disk.
Listing Installed Plugins
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...
$
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/opt/shibboleth-idp/bin/plugin.sh
...
-l
...
or
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C:>\opt\shibboleth-idp\bin\plugin.bat
...
-l