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<p class="MsoNormal">For the Implicit Flow, the “nonce” description contains this text at
<a href="http://openid.bitbucket.org/openid-connect-core-1_0.html#ImplicitAuthorizationRequest">
http://openid.bitbucket.org/openid-connect-core-1_0.html#ImplicitAuthorizationRequest</a>:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN" style="font-family:"Verdana","sans-serif";color:black">Sufficient entropy MUST be present in the
</span><tt><span lang="EN" style="font-size:12.0pt">nonce</span></tt><span lang="EN" style="font-family:"Verdana","sans-serif";color:black"> values used to prevent attackers from guessing values.
<span style="background:yellow;mso-highlight:yellow">One method to achieve this is to store a random value as a signed session cookie, and pass the value in the
</span></span><tt><span lang="EN" style="font-size:12.0pt;background:yellow;mso-highlight:yellow">nonce</span></tt><span lang="EN" style="font-family:"Verdana","sans-serif";color:black;background:yellow;mso-highlight:yellow"> parameter. In that case, the
</span><tt><span lang="EN" style="font-size:12.0pt;background:yellow;mso-highlight:yellow">nonce</span></tt><span lang="EN" style="font-family:"Verdana","sans-serif";color:black;background:yellow;mso-highlight:yellow"> in the returned ID Token can be compared
to the signed session cookie to detect ID Token replay by third parties.</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">George wrote this about the suggestion in his review:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">“I'm not sure this suggestion makes sense for the implicit flow. The client would need to write a cookie value on the domain of the redirect_uri and the attempt to read it on the return of the implicit flow. Wondering
if a local storage example would make more sense.”<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Do people agree with him? If so, does someone want to supply specific alternative text to use?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> -- Mike<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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