Thursday, September 14, 2017

Exchanging SAML2 Bearer Tokens with OAuth2 using WSO2 API Manager 2.1.0

In this article I am demonstrating how to exchange a SAML2 assertion to an OAuth2 access token using WSO2 API Manager 2.1.0 version.

You can refer the WSO2 official documentation [1] for more information on the same topic.

Here, I am not using any client application which gets authenticated with WSO2 API Manager with SAML 2.0 protocol, instead I am generating a valid SAML assertion using a command line tool. You can find the download link of this CLI tool in [1].

Once you download the ZIP file of the tool, extract it and navigate to the extracted folder from command line.

Then you need to execute the following command. For descriptions for each parameter, you can [1].


java -jar SAML2AssertionCreator.jar <Identity_Provider_Entity_Id> <NameId value of in the subject of SAML assertion> <Recipient> <Audience> <Identity_Provider_JKS_file> <Identity_Provider_JKS_password> <Identity_Provider_certificate_alias> <Identity_Provider_Private_private_key_password>

So, here’s the command I run that has the values which I use.

java -jar SAML2AssertionCreator.jar localhost admin https://localhost:9443/oauth2/token https://localhost:9443/oauth2/token /home/tharindu/wso2am-2.1.0/repository/resources/security/wso2carbon.jks wso2carbon wso2carbon wso2carbon

In above command, I have added ‘localhost’ for Identity_Provider_Entity_Id. The reason for that is, the default Identity Provider (also known as Resident IDP) in API Manager is ‘localhost’. As the NameId value in the subject of SAML assertion, I have used ‘admin’ because the username I try this scenario against is ‘admin’. For Recipient, I have added https://localhost:9443/oauth2/token which is the OAuth 2 Token Endpoint of API Manager which will receive this SAML assertion once I forward it later. For Audience, I have added the same OAuth 2 Token Endpoint URL of API Manager, because this SAML assertion should be consumed by API Manager for exchanging it to an OAuth 2 token later. Then I have pointed out the wso2carbon.jks file of the API Manager which is the primary keystore of the API Manager. This is the place where the private key will be taken for signing the SAML Assertion that this tool generates. Then I have added the password of this keystore file, which is ‘wso2carbon’ by default. Then, the default certificate alias of WSO2 API Manager is ‘wso2carbon’ and the password of the default private key of API Manager is again ‘wso2carbon’. I have added those values in the command respectively.

Here’s the output I get after running the above command. First it shows the plain XML SAML assertion. After that it shows the URL Encoded value of the Base64 encoded assertion.(added newlines for readability)

Assertion String: <?xml version="1.0" encoding="UTF-8"?><saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" ID="bmnnphkklnpdbkhddabajfegocdknlemffdimbpc" IssueInstant="2017-09-14T21:17:20.305Z" Version="2.0"><saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">localhost</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="#bmnnphkklnpdbkhddabajfegocdknlemffdimbpc">
<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#"><ec:InclusiveNamespaces xmlns:ec="http://www.w3.org/2001/10/xml-exc-c14n#" PrefixList="ds saml xs xsi"/></ds:Transform>
</ds:Transforms>
<ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<ds:DigestValue>OqZVvZeDvEp+sh+XD4t1jBFgY00=</ds:DigestValue>
</ds:Reference>
</ds:SignedInfo>
<ds:SignatureValue>
IQSI8Tt+NBtgpVq1c7q774Nr9NvjCj12HjBW6CAjaD/pJvnf29uQhFEYMZzH5/8f6enyG99ygAJC
hNCLz/BNj2DEZYX9ZniPc+4QhtY4jDrS+0NvAApRV7374cTHjT5L32NkFzu+u37vTqhEyKaWpwGm
bRNXy/MwDjgfxvrZxoU=
</ds:SignatureValue>
<ds:KeyInfo><ds:X509Data><ds:X509Certificate>MIICNTCCAZ6gAwIBAgIES343gjANBgkqhkiG9w0BAQUFADBVMQswCQYDVQQGEwJVUzELMAkGA1UE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=</ds:X509Certificate></ds:X509Data></ds:KeyInfo></ds:Signature><saml:Subject><saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress">admin</saml:NameID><saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer"><saml:SubjectConfirmationData InResponseTo="0" NotOnOrAfter="2017-09-14T21:22:20.305Z" Recipient="https://localhost:9443/oauth2/token"/></saml:SubjectConfirmation></saml:Subject><saml:Conditions NotBefore="2017-09-14T21:17:20.305Z" NotOnOrAfter="2017-09-14T21:22:20.305Z"><saml:AudienceRestriction><saml:Audience>https://localhost:9443/oauth2/token</saml:Audience></saml:AudienceRestriction></saml:Conditions><saml:AuthnStatement AuthnInstant="2017-09-14T21:17:20.353Z"><saml:AuthnContext><saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:Password</saml:AuthnContextClassRef></saml:AuthnContext></saml:AuthnStatement><saml:AttributeStatement><saml:Attribute><saml:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">/</saml:AttributeValue></saml:Attribute></saml:AttributeStatement></saml:Assertion>

base64-url Encoded Assertion String: PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz48c2FtbDpBc3NlcnRp
b24geG1s%0AbnM6c2FtbD0idXJuOm9hc2lzOm5hbWVzOnRjOlNBTUw6Mi4wOmFzc2VydGlvbiIgSUQ9ImJtbm5w%0AaGtr
bG5wZGJraGRkYWJhamZlZ29jZGtubGVtZmZkaW1icGMiIElzc3VlSW5zdGFudD0iMjAxNy0w%0AOS0xNFQyMToxNzoyMC4
zMDVaIiBWZXJzaW9uPSIyLjAiPjxzYW1sOklzc3VlciBGb3JtYXQ9InVy%0AbjpvYXNpczpuYW1lczp0YzpTQU1MOjIuMDpuYW1la
WQtZm9ybWF0OmVudGl0eSI%2BbG9jYWxob3N0%0APC9zYW1sOklzc3Vlcj48ZHM6U2lnbmF0dXJlIHhtbG5zOmRzPSJodHRw
Oi8vd3d3LnczLm9yZy8y%0AMDAwLzA5L3htbGRzaWcjIj4KPGRzOlNpZ25lZEluZm8%2BCjxkczpDYW5vbmljYWxpemF0aW9uT
WV0%0AaG9kIEFsZ29yaXRobT0iaHR0cDovL3d3dy53My5vcmcvMjAwMS8xMC94bWwtZXhjLWMxNG4jIi8%2B%0ACjxkczpTaWd
uYXR1cmVNZXRob2QgQWxnb3JpdGhtPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwLzA5%0AL3htbG
RzaWcjcnNhLXNoYTEiLz4KPGRzOlJlZmVyZW5jZSBVUkk9IiNibW5ucGhra2xucGRia2hk%0AZGFiYWpmZWdvY2RrbmxlbW
ZmZGltYnBjIj4KPGRzOlRyYW5zZm9ybXM%2BCjxkczpUcmFuc2Zvcm0g%0AQWxnb3JpdGhtPSJodHRwOi8vd3d3LnczLm9y
Zy8yMDAwLzA5L3htbGRzaWcjZW52ZWxvcGVkLXNp%0AZ25hdHVyZSIvPgo8ZHM6VHJhbnNmb3JtIEFsZ29yaXRobT0iaHR
0cDovL3d3dy53My5vcmcvMjAw%0AMS8xMC94bWwtZXhjLWMxNG4jIj48ZWM6SW5jbHVzaXZlTmFtZXNwYWNlcyB4bWxuczplYz0ia
HR0%0AcDovL3d3dy53My5vcmcvMjAwMS8xMC94bWwtZXhjLWMxNG4jIiBQcmVmaXhMaXN0PSJkcyBzYW1s%0AIHhzIHhzaSIvPjwvZ
HM6VHJhbnNmb3JtPgo8L2RzOlRyYW5zZm9ybXM%2BCjxkczpEaWdlc3RNZXRo%0Ab2QgQWxnb3JpdGhtPSJodHRwOi8vd3d3LnczLm9
yZy8yMDAwLzA5L3htbGRzaWcjc2hhMSIvPgo8%0AZHM6RGlnZXN0VmFsdWU%2BT3FaVnZaZUR2RXArc2grWEQ0dDFqQkZnWTAwPTw
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ASVFTSThUdCtOQnRncFZxMWM3cTc3NE5yOU52akNqMTJIakJXNkNBamFEL3BKdm5mMjl1UWhGRVlN%0AWnpINS84ZjZlbnlHOTl5Z0FKQ
wpoTkNMei9CTmoyREVaWVg5Wm5pUGMrNFFodFk0akRyUyswTnZB%0AQXBSVjczNzRjVEhqVDVMMzJOa0Z6dSt1Mzd2VHFoRXlLYVdwd0dtC
mJSTlh5L013RGpnZnh2clp4%0Ab1U9CjwvZHM6U2lnbmF0dXJlVmFsdWU%2BCjxkczpLZXlJbmZvPjxkczpYNTA5RGF0YT48ZHM6WDUw%0AOU
NlcnRpZmljYXRlPk1JSUNOVENDQVo2Z0F3SUJBZ0lFUzM0M2dqQU5CZ2txaGtpRzl3MEJBUVVG%0AQURCVk1Rc3dDUVlEVlFRR0V3SlZVekVMTU
FrR0ExVUUKQ0F3Q1EwRXhGakFVQmdOVkJBY01EVTF2%0AZFc1MFlXbHVJRlpwWlhjeERUQUxCZ05WQkFvTUJGZFRUekl4RWpBUUJnTlZCQU1
NQ1d4dgpZMkZz%0AYUc5emREQWVGdzB4TURBeU1Ua3dOekF5TWpaYUZ3MHpOVEF5TV
RNd056QXlNalphTUZVeEN6QUpC%0AZ05WQkFZVEFsVlRNUXN3CkNRWURWUVFJREFKRFFURVdNQlFHQTFVRUJ
3d05UVzkxYm5SaGFXNGdW%0AbWxsZHpFTk1Bc0dBMVVFQ2d3RVYxTlBNakVTTUJBR0ExVUUKQXd3SmJHOWpZV
3hvYjNOME1JR2ZN%0AQTBHQ1NxR1NJYjNEUUVCQVFVQUE0R05BRENCaVFLQmdRQ1VwL29WMXZXYzgvVGtRU2
lBdlRvdQpz%0ATXpPTTRhc0IyaWx0cjJRS296bmk1YVZGdTgxOE1wT0xaSXI4TE1uVHpXbGxKdnZhQTVSQUFkcGJF%
0AQ2IrNDhGamJCZTBoc2VVZE41Ckhwd3ZuSC9EVzhaY2NHdms1M0k2T3JxN2hMQ3YxWkh0dU9Db2tn%0AaHovQVR
yaHlQcStRa3RNZlhuUlM0SHJLR0pUenhhQ2NVN09RSUQKQVFBQm94SXdFREFPQmdOVkhR%0AOEJ
BZjhFQkFNQ0JQQXdEUVlKS29aSWh2Y05BUUVGQlFBRGdZRUFXNXdQUjdjcjFMQWRxK0lyUjQ0%0AaQpRbFJHNUlU
Q1pYWTloSTBQeWdMUDJySEFOaCtQWWZUbXhidU9ueWtOR3loTTZGakZMYlcydVpI%0AUVRZMWpNclBwcmpPcm1
5SzVzakpSCk80ZDFEZUdIVC9ZbklqczlKb2dSS3Y0WEhFQ3dMdElWZEFi%0ASWRXSEV0VlpKeU1Ta3RjeXlzRmN2dWh
QUUs4UWMvRS9XcTh1SFNDbz08L2RzOlg1MDlDZXJ0aWZp%0AY2F0ZT48L2RzOlg1MDlEYXRhPjwvZHM6S2V5SW5
mbz48L2RzOlNpZ25hdHVyZT48c2FtbDpTdWJq%0AZWN0PjxzYW1sOk5hbWVJRCBGb3JtYXQ9InVybjpvYXNpczpuYW
1lczp0YzpTQU1MOjEuMTpuYW1l%0AaWQtZm9ybWF0OmVtYWlsQWRkcmVzcyI%2BYWRtaW48L3NhbWw6TmFtZUlE
PjxzYW1sOlN1YmplY3RD%0Ab25maXJtYXRpb24gTWV0aG9kPSJ1cm46b2FzaXM6bmFtZXM6dGM6U0FNTDoyLjA6Y
206YmVhcmVy%0AIj48c2FtbDpTdWJqZWN0Q29uZmlybWF0aW9uRGF0YSBJblJlc3BvbnNlVG89IjAiIE5vdE9uT3JB%0A
ZnRlcj0iMjAxNy0wOS0xNFQyMToyMjoyMC4zMDVaIiBSZWNpcGllbnQ9Imh0dHBzOi8vbG9jYWxo%0Ab3N0Ojk0NDMvb
2F1dGgyL3Rva2VuIi8%2BPC9zYW1sOlN1YmplY3RDb25maXJtYXRpb24%2BPC9zYW1s%0AOlN1YmplY3Q%2BPHNhb
Ww6Q29uZGl0aW9ucyBOb3RCZWZvcmU9IjIwMTctMDktMTRUMjE6MTc6MjAu%0AMzA1WiIgTm90T25PckFmdGVyPSI
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OkF1ZGllbmNlUmVzdHJpY3Rpb24%2BPC9zYW1s%0AOkNvbmRpdGlvbnM%2BPHNhbWw6QXV0aG5TdGF0ZW1lbnQgQXV0aG5JbnN0YW50
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Now that we have the SAML assertion, next step is to send it to API Manager for exchanging it with an OAuth 2 token.

For that, we need to have a valid credentials (Client ID and Client Secret) of an OAuth App registered in API Manager. Here I am creating a Service Provider in the Management Console of API Manager.


Then in the Service Provider configuration, I configure the OAuth app settings.


Here, the important setting is ‘SAML2’ checkbox, which tells API Manager that this application should support SAML Bearer Grant Type. In the settings, the ‘Callback Url’ is a mandatory field, although it has no use when comes to SAML Bearer Grant Type. It is only useful for Authorization Code Grant Type. But since the textbox is mandatory, I’ll insert a dummy value there and continue.

Now it will show the generated Client ID and Client Secret values which I can use now for exchanging the SAML assertion to an OAuth access token
.

Now that I have all the parameters I need, here I call the Token API URL of WSO2 API Manager, which is https://localhost:8243/token . T

curl -k -d "grant_type=urn:ietf:params:oauth:grant-type:saml2-bearer&assertion=<base64-URL_encoded_assertion>&scope=PRODUCTION" -H "Authorization: Basic <base64_encoded_consumer-key:consumer_secret>" -H "Content-Type: application/x-www-form-urlencoded" https://localhost:8243/token



In the response, we get a JSON message from API Manager, which contains the OAuth 2 access token.

{
  "access_token":"ab80696d-e309-3b0a-994b-a08785fea305",
  "refresh_token":"3263eede-3c8b-3917-9e0b-04f26a96a87f",
  "scope":"default",
  "token_type":"Bearer",
  "expires_in":3600
}

Using this OAuth 2 access token, we can invoke any API hosted in WSO2 API Manager, provided that the particular APIs we call are subscribed by the OAuth app we used here (the app which we took Client ID and Client Secret values).

Error Handling

When you try the above flow, there can be different cases which would go wrong. In such case, enabling the DEBUG logs in the API Manager would help you to isolate the exact issue. For that, add the following two lines to API_Manager/repository/conf/log4j.properties file and restart the server.


log4j.logger.org.wso2.carbon.identity.oauth=DEBUG
log4j.logger.org.wso2.carbon.identity.oauth2=DEBUG

After that if you get an error, you can refer the debug logs to get some clue on the issue.

Most of the time, you would see a common error as following, which doesn’t explain the exact problem.

{"error_description":"Provided Authorization Grant is invalid","error":"invalid_grant"}

One case this flow might break is when the SAML assertion you use is an already expired one.

In the wso2carbon.log of API Manager, following debug log can be seen which explains the issue.

[2017-09-14 15:00:34,612] DEBUG - SAML2BearerGrantHandler NotOnOrAfter is having an expired timestamp in Conditions element

Another case would be when the SAML Issuer name you used to generate the SAML assertion is not known by API Manager. In that case, still you would see the same error as above, but in the DEBUG log it would have following, which explains the issue.

[2017-09-14 15:07:25,024] DEBUG - SAML2BearerGrantHandler SAML Token Issuer : myidp not registered as a local Identity Provider in tenant : carbon.super

Another case when the value you have in the SAML assertion for Audience is not matching with API Manager’s Audience.

[2017-09-14 15:13:08,737] DEBUG - SAML2BearerGrantHandler SAML Assertion Audience Restriction validation failed against the Audience : https://localhost:9443/oauth2/token of Identity Provider : LOCAL in tenant : carbon.super

Another case is when the Recipient you have in the SAML assertion is not matching with the Recipient value of API Manager. That again can be identified using the debug log which is below.

DEBUG - SAML2BearerGrantHandler None of the recipient URLs match against the token endpoint alias : https://localhost:9443/oauth2/token of Identity Provider LOCAL in tenant : carbon.super

Likewise we can use the debug logs to identify most of the issues that would come during this flow.

References



Tharindu Edirisinghe
Platform Security Team
WSO2

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