<p></p>
<p>I think <a href="https://tools.ietf.org/html/rfc8252#section-7.3" rel="nofollow">https://tools.ietf.org/html/rfc8252#section-7.3</a> would be relevant here. Note the following requirement regarding 127.0.0.1:</p>
<blockquote>
<p>The authorization server MUST allow any port to be specified at the<br>
time of the request for loopback IP redirect URIs, to accommodate<br>
clients that obtain an available ephemeral port from the operating<br>
system at the time of the request.</p>
</blockquote>
<p>I'm not sure if doorkeeper already allows any port for loopback communication.</p>
<p>Section 7.1 ("Private-Use URI Scheme Redirection") also seems interesting for mobile apps. It would be good if more mobile app devs could join this discussion, to see what requirements they have.</p>

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