SAML Single logout through OKTA

I have got the following SP's Request and IDP's reponse:

<samlp:LogoutRequest xmlns="urn:oasis:names:tc:SAML:2.0:metadata" Destination="https://dev-nnn.oktapreview.com/app/somename_hped800eportal_1/exk8dlkd0tCutHWlj0h7/slo/saml" ID="_af6eaa4a-9d5b-41ce-b265-d39dfdc5248e" Version="2.0" IssueInstant="2016-10-14T12:31:59Z" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"><saml:Issuer xmlns:saml="http://www.w3.org/2005/Atom">https://HPED800E:444/SynPortal/login.aspx</saml:Issuer><saml:NameID xmlns:saml="urn:oasis:names:tc:SAML:2.0:nameid-format:unspecified">CDA_Main\hjami</saml:NameID><samlp:SessionIndex>_d9f07562-3a7f-4c03-a62d-8a985f34058f</samlp:SessionIndex><Signature xmlns="http://www.w3.org/2000/09/xmldsig#"><SignedInfo><CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" /><SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" /><Reference URI=""><Transforms><Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /></Transforms><DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" /><DigestValue>bBbMvzSjRc0zc1jtIxmqmkO4bYo=</DigestValue></Reference></SignedInfo><SignatureValue>...5g==</SignatureValue><KeyInfo><X509Data><X509Certificate>...Cw==</X509Certificate></X509Data></KeyInfo></Signature></samlp:LogoutRequest>

<?xml version="1.0" encoding="UTF-8"?><saml2p:LogoutResponse xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="https://hped800e:444/SynPortal/logout.aspx" ID="id50277036872307661186452042" InResponseTo="_1eef2809-b49e-412e-a0c5-3596e3c0b158" IssueInstant="2016-10-14T00:32:05.949Z" Version="2.0"><saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">http://www.okta.com/exk8dlkd0tCutHWlj0h7</saml2:Issuer><ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"><ds:SignedInfo><ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/><ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/><ds:Reference URI="#id50277036872307661186452042"><ds:Transforms><ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/><ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/></ds:Transforms><ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/><ds:DigestValue>3k7z8GF3kBemyYm+6+mEbZMSAYw=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>...MA==</ds:SignatureValue><ds:KeyInfo><ds:X509Data><ds:X509Certificate>...VNm</ds:X509Certificate></ds:X509Data></ds:KeyInfo></ds:Signature><saml2p:Status xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol"><saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:AuthnFailed"/></saml2p:Status></saml2p:LogoutResponse>

the request is encoded base-64 and then sent via post binding. I am getting the AuthnFailed response.

I have set up only one sp for the IDP for simplicity. Does anyone know what I am doing wrong here?

This information is insufficient to determine as what has gone wrong in your implementation for single logout. Can you please provide following information

1) Your single logout settings in Okta that can be found under SAML Settings -> Advanced Settings under General tab of your app?

2) Based on above settings please make sure you have uploaded certificate to Okta?

3) Which SAML toolkit are you using? Can you provide toolkit settings for your toolkit?

See the working SLO request below.

<samlp:LogoutRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
ID="_d2be8c5de3aeeeac27c8xxxxyyyy"
Version="2.0"
IssueInstant="2016-04-27T16:15:06Z"
Destination="https://org-name.okta.com/app/simplesamlphpexample/exk4xxyyPcvdVq70x7/slo/saml"
>
<saml:Issuer>http://localhost:8888/simplesamlphp/www/module.php/saml/sp/metadata.php/example-okta-com</saml:Issuer>
<ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
    <ds:SignedInfo>
        <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
        <ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" />
        <ds:Reference URI="#_d1be8c5dc2aeeeac27c8daf04b7xxxyyy6b36287bd6">
            <ds:Transforms>
                <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
                <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
            </ds:Transforms>
            <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
            <ds:DigestValue>{{some_value}}</ds:DigestValue>
        </ds:Reference>
    </ds:SignedInfo>
    <ds:SignatureValue>{{some_value}}</ds:SignatureValue>
    <ds:KeyInfo>
        <ds:X509Data>
            <ds:X509Certificate>{{some_value}}</ds:X509Certificate>
        </ds:X509Data>
    </ds:KeyInfo>
</ds:Signature>
<saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified">{{email}}</saml:NameID>
<samlp:SessionIndex>{{some_value}}</samlp:SessionIndex>

Comparing the SLO settings for your request and mine few things stood out.

1) CanonicalizationMethod Algorithm in my case is set to http://www.w3.org/2001/10/xml-exc-c14n#. Yours is http://www.w3.org/TR/2001/REC-xml-c14n-20010315.

2) Name ID in your case is "CDA_Main\hjami". Can you please let me know which attribute in Okta is this? Also, have you overridden the userName of your app using the mappings from Okta to app (under profile editor -> your app mappings). For example, I am overriding the app userName from Okta login/email to be custom attribute.

If you are using another attribute (whose value is set to CDA_Main\hjami) from Okta as the username of the app, please make sure that you are overriding it like I am doing in the screenshot above.