Extension-Id available via REST-call?

In the storage format of a forge macro we see something like this:

<ac:adf-node type="extension">
        <ac:adf-attribute key="extension-type">com.atlassian.ecosystem</ac:adf-attribute>
        <ac:adf-attribute key="extension-key">1111111-1111-111-1111/1111111-1111-111-1111c/static/navigation-macro</ac:adf-attribute>
        <ac:adf-attribute key="parameters">
            <ac:adf-parameter key="local-id">81bca038-df48-413c-aab9-c10af41864f9</ac:adf-parameter>
            <ac:adf-parameter key="extension-id">ari:cloud:ecosystem::extension/1111111-1111-111-1111/1111111-1111-111-1111/static/navigation-macro</ac:adf-parameter>
            <ac:adf-parameter key="extension-title">Navigation (Development)</ac:adf-parameter>
        </ac:adf-attribute>
        <ac:adf-attribute key="text">Navigation (Development)</ac:adf-attribute>
        <ac:adf-attribute key="layout">default</ac:adf-attribute>
        <ac:adf-attribute key="local-id">1111111-1111-111-1111</ac:adf-attribute>
    </ac:adf-node>
    <ac:adf-fallback>
        <ac:adf-node type="extension">
            <ac:adf-attribute key="extension-type">com.atlassian.ecosystem</ac:adf-attribute>
            <ac:adf-attribute key="extension-key">1111111-1111-111-1111/1111111-1111-111-1111/static/navigation-macro</ac:adf-attribute>
            <ac:adf-attribute key="parameters">
                <ac:adf-parameter key="local-id">1111111-1111-111-1111</ac:adf-parameter>
                <ac:adf-parameter key="extension-id">ari:cloud:ecosystem::extension/1111111-1111-111-1111/1111111-1111-111-1111/static/navigation-macro</ac:adf-parameter>
                <ac:adf-parameter key="extension-title">Navigation (Development)</ac:adf-parameter>
            </ac:adf-attribute>
            <ac:adf-attribute key="text">Navigation (Development)</ac:adf-attribute>
            <ac:adf-attribute key="layout">default</ac:adf-attribute>
            <ac:adf-attribute key="local-id">1111111-1111-111-1111</ac:adf-attribute>
        </ac:adf-node>
    </ac:adf-fallback>
</ac:adf-extension>

It is required for this project to programmatically post the storage format of a macro onto a confluence-page. However for this I would need the string contained in the property “Extension-Id” or “Extension-key”. The first part consists of the app-id which we have at our disposal but what is the second part behind the slash? Can you somehow obtain it with a REST-call?

Thank you very much and excuse my english