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    Hi Linus,<br>
    <br>
    I agree there may be some issues introduced by Mutual TLS.<br>
    <br>
    However, in principle, access tokens are bearer tokens and there
    really is no<br>
    implicit control on what entity is using the access token.<br>
    <br>
    For example, if the oauth client trusts RS-1 to deliver a service,
    then<br>
    it should trust RS-1 to use the token to access RS-2.<br>
    <br>
    Possibly Mutual TLS could be extended to cover the RS-1<->RS-2
    connection<br>
    as well.<br>
    <br>
      Thanks,<br>
      Rich<br>
    <br>
    <br>
    <div class="moz-cite-prefix">On 10/17/2017 3:19 PM, Linus
      Lewandowski wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAB96meb+mY_0B-44TdxJ2YyXMn433HJNiTyw687bAfTz-kY8VQ@mail.gmail.com">
      <div dir="ltr">Hi,
        <div><br>
        </div>
        <div>This won't really be possible with Mutual TLS <<a
href="https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_id_draft-2Dietf-2Doauth-2Dmtls-2D03.html&d=DwMFaQ&c=RoP1YumCXCgaWHvlZYR8PQcxBKCX5YTpkKY057SbK10&r=nNxUKneeZofWTyt9qclOUTeEg29NkEkknFyDupoNiiA&m=tb9zOhjteWWIATXzVc3HJCrh6hqsYhws1Yn11x8GiBg&s=GTdDEw8rKcAS_akoL4N2C8PYXbN8wG3H4JtBMenjwjA&e="
            target="_blank" moz-do-not-send="true">https://tools.ietf.org/id/draft-ietf-oauth-mtls-03.html</a>></div>
        <div><br>
        </div>
        <div>Without Mutual TLS, this means that RS-1 can impersonate
          your app when talking to RS-2, and RS-2 when talking to RS-1.
          Not ideal from the security POV.</div>
        <div><br>
        </div>
        <div>Regards,<br>
          Linus</div>
        <br>
        <div class="gmail_quote">
          <div dir="ltr">On Tue, Oct 17, 2017 at 9:04 PM rich levinson
            via Openid-specs-ab <<a
              href="mailto:openid-specs-ab@lists.openid.net"
              target="_blank" moz-do-not-send="true">openid-specs-ab@lists.openid.net</a>>
            wrote:<br>
          </div>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">
            <div text="#000000" bgcolor="#FFFFFF"> Does anyone have
              guidance on validity of the following scenario?:<br>
              <blockquote>There is a Resource Server, RS-1, that, in
                order to provide its service<br>
                needs to also access a downstream Resource Server RS-2.<br>
                <br>
                When the oauth client requests an access token, it is
                granted an access token<br>
                by the az-svr (that knows that both RS-1 and RS-2 must
                be used) that<br>
                contains 2 audiences: RS-1 and RS-2.<br>
                <br>
                The oauth client uses the access token to access RS-1.<br>
                <br>
                RS-1, in turn, uses the same access token to access
                RS-2.<br>
                <br>
                The response is returned from RS-2 to RS-1.<br>
                RS-1 combines the response from RS-2 w its own resp and<br>
                 returns the combined response to the oauth client.<br>
              </blockquote>
              Given that the token is a bearer token it seems to me
              there is no reason why<br>
              both the oauth client AND the RS-1 can't use the access
              token to get what they<br>
              need, w/o RS-1 having to register itself as a separate
              client and get its own<br>
              access token.<br>
              <br>
              So, the question is whether this is a legitimate use case
              for a resource server<br>
              to access downstream services.<br>
              <br>
                Thanks,<br>
                Rich<br>
              <br>
            </div>
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          </blockquote>
        </div>
      </div>
    </blockquote>
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