Ushani Balasooriya's Blog: Mediation Extension

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Tuesday, February 7, 2017

How to convert a json/xml payload in to a backend accepts form data payload in APIM

Imagine you have a scenario, where a user sens a json or xml payload via client eventhough the backend accepts only formdata. So you need to find a method to change the payload during the mediation without editing the API synapse configuration manualy.

E.g.,

{

"userid": "123abc",

"name": "Ushani",

"address ": "Colombo"

}

in to

userid=123sbc&name=ushani&address=Colombo

You can simply achieve this by adding a custom mediation extension in to in flow since the default available mediation extensions do not support it.

In order to do this you have change the Content Type in to application/x-www-form-urlencoded.

Sample mediation extension :

<?xml version="1.0" encoding="UTF-8"?>
<sequence xmlns="http://ws.apache.org/ns/synapse" name="formdataconvert"> 
      <property name="messageType" value="application/x-www-form-urlencoded" scope="axis2" type="STRING"/> 
   <log level="full"/>
</sequence>

How to perform an action based on a JWT claim value in APIM 2.0

To achieve this, We can use custom mediation extensions in APIM 2.0. For more details on Custom mediation, please have a look at this document [1].

When you write your custom sequence, below I have given the synapse source and explanation. In this example, we are going to do our action based on the claim value enduser as an example.

1. First we have set the X-JWT-Assertion header value in to a property named authheader.

Sample X-JWT-Assertion is as below :

X-JWT-Assertion = eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsIng1dCI6ImFfamhOdXMyMUtWdW9GeDY1TG1rVzJPX2wxMCJ9.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.FE2luGlWKZKZBVjsx7beA4WVlLFJSoHNGgJKm56maK7qddleEzTi/QhDAdyC47dW+RgkaJZLSgdvM6ROyW890io7QCOqjJZg7KnlB54qh2DBoBmAnYbmFZAC08nxnAGpeiy6W4YkYMWlJNW+lw5D3b3I4NOhyhsIStA9ec9TSQA=

2. Then we have used a script mediator to split and decode our value from the authheader.

var temp_auth = mc.getProperty('authheader').trim();

var val = new Array();

val= temp_auth.split("\\.");

By the above javascript, we have split the value we get by "." I have highlighted it by Yellow color.

Grean colored value has got our JWT claims.

3. Then we access the 2nd value as val[1] and decode it using Base64.

var auth=val[1];

var jsonStr = Packages.java.lang.String(Packages.org.apache.axiom.om.util.Base64.decode(auth), "UTF-8");

If you decode the particular value using a base64, you wil be able to see the below value.

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

{"http:\/\/wso2.org\/claims\/applicationtier":"Unlimited",

"http:\/\/wso2.org\/claims\/keytype":"PRODUCTION",

"http:\/\/wso2.org\/claims\/version":"1.0.0",

"iss":"wso2.org\/products\/am",

"http:\/\/wso2.org\/claims\/applicationname":"DefaultApplication",

"http:\/\/wso2.org\/claims\/enduser":"admin@carbon.super",

"http:\/\/wso2.org\/claims\/enduserTenantId":"-1234",

"http:\/\/wso2.org\/claims\/subscriber":"admin",

"http:\/\/wso2.org\/claims\/tier":"Unlimited",

"http:\/\/wso2.org\/claims\/applicationid":"1",

"http:\/\/wso2.org\/claims\/usertype":"APPLICATION",

"exp":1486459587,

"http:\/\/wso2.org\/claims\/apicontext":"\/jwtapi\/1.0.0"}

4. Since we get the claims values with an escape character, we need to replace the "/" with a blank.

This is the actual value we get : "http:\/\/wso2.org\/claims\/enduser":"admin@carbon.super",

Replace function : jsonStr=jsonStr.replace("\\", "");

After Replace : "http://wso2.org/claims/enduser":"admin@carbon.super",

5. Then if we need to perform our acceptation and rejection based on enduser value as we have decided, we should split the enduser value by the below claim. You can use any claim value from the above.

var tempStr = new Array();

tempStr= jsonStr.split('http://wso2.org/claims/enduser\":\"');

6. We have split it in to 2 values. So the rest of the value after the enduser claim which is in tempStr[1], we split again to retrieve only the enduser value which is admin@carbon.super.

Value needs to be split :

admin@carbon.super",

"http://wso2.org/claims/enduserTenantId":"-1234",

"http://wso2.org/claims/subscriber":"admin",

"http://wso2.org/claims/tier":"Unlimited",

"http://wso2.org/claims/applicationid":"1",

"http://wso2.org/claims/usertype":"APPLICATION",

var decoded = new Array();

decoded = tempStr[1].split("\"");

7. To access the enduser value in our synapse level, we need to set the decoded enduser value in to message context as below by setting it as a property. I have set it as username.

setProperty(String key, Object value)

Set a custom (local) property with the given name on the message instance

mc.setProperty("username",decoded[0]);

8. Then use a filter mediator to perform action based on the username. In here, I have logged a message if the username = admin@carbon.super and dropped the request if it is another user. For more information on Filter mediator, please have a look at this [2]

<?xml version="1.0" encoding="UTF-8"?> <filter source="get-property('username')" regex="admin@carbon.super"> <then> <log level="custom"> <property name="accept" value="Accept the message" /> </log> </then> <else> <drop /> </else> </filter>

9. I have uploaded my custom mediation extension via publisher as given in the below screen. You have to republish the API once you save it, if it is already published.

So my complete mediation extension is as below :

<sequence xmlns="http://ws.apache.org/ns/synapse" name="JWTDec">
    <log level="custom">
      <property name="X-JWT-Assertion" expression="get-property('transport','X-JWT-Assertion')"/>
    </log>
  <property name="authheader" expression="get-property('transport','X-JWT-Assertion')" scope="default" type="STRING" description="get X-JWT-Assertion header"/>
            <script language="js" description="extract username">
  var temp_auth = mc.getProperty('authheader').trim();
                var val = new Array();
                val= temp_auth.split("\\.");
                var auth=val[1];
                var jsonStr = Packages.java.lang.String(Packages.org.apache.axiom.om.util.Base64.decode(auth), "UTF-8");
                jsonStr=jsonStr.replace("\\", "");
                var tempStr = new Array();
                tempStr= jsonStr.split('http://wso2.org/claims/enduser\":\"');
                var decoded = new Array();
                decoded = tempStr[1].split("\"");
  mc.setProperty("username",decoded[0]);
  </script>
   
         <log level="custom">
       <property name="username" expression="get-property('username')"/>
     </log> 

                <filter source="get-property('username')" regex="admin@carbon.super">
                     <then>
                    <log level="custom">
                      <property name="accept" value="Accept the message"/>
                    </log>
                 </then>
                 <else>
                   <drop/>
                 </else>
               </filter>

        
</sequence>

[1] https://docs.wso2.com/display/APICloud/Change+the+Default+Mediation+Flow+of+API+Requests

[2] https://docs.wso2.com/display/ESB500/Filter+Mediator

Sunday, January 29, 2017

How to send custom header in soap message when invoking an API in APIM 2.0 without using a client

Introduction :

WSO2 APIM has 2 methods of securing backend. Basic Auth and Digest Auth. So if the backend expects a security like WSSE security Username Authentication, there should be a method to apply security header.

Possible method is to send the particular authentication credentials via a client. But it is clear that the secured backend credentials cannot be shared with API subscribers when they expose the backend via WSO2 APIM endpoint. So the best thing is to customize the soap message in this scenario in the middle of the mediation.

This can be achieved via a mediation logic which can be done via a custom mediation handler or mediation extension.

If you do not want to restart the server, best thing is to use a mediation extension which you can also upload via UI, in WSO2 API Manager publisher.

One more important thing is, configuring these credentials as you can easily change at anypoint.

This is achieved by adding them as a registry property.

Below explains a sample Mediation extension written to achieve this.

The client user name and password are encapsulated in a WS-Security <wsse:UsernameToken>. When the Enterprise Gateway receives this token, it can perform one of the following tasks, depending on the requirements:

-Ensure that the timestamp on the token is still valid

-Authenticate the user name against a repository

-Authenticate the user name and password against a repository

The given extension is to enrich this soap request to achieve the 3rd task.

This extension is written to inject username token in the message mediation, when client invokes an API in APIM 2.0 which has a SOAP endpoint which is secured using WS-Security and requires User Name Token header to appear on the SOAP headers.

This is done using Enrich mediator and payload mediator.

Enrich mediator is used to remove the existing soap header by copying the soap body.

Payload mediator constructs the soap header with username token tag and security header.

Username and password is taken from a registry resource property by an expression.

Pre-Requisites :

1. Add username and password as properties in registry under resources _system/config/users

username : <username>
password : <password>

Steps :

1. In this scenario API should be created as api with version 1.0.0 by admin user.

Mediation Extension named as : admin--api:v1.0.0--In

<?xml version="1.0" encoding="UTF-8"?>
<sequence xmlns="http://ws.apache.org/ns/synapse" name="admin--api:v1.0.0--In"> 
   <enrich>
      <source type="body" clone="true"/>
      <target type="property" property="ORIGINAL_BODY"/>
   </enrich> 
   <payloadFactory media-type="xml">
      <format>
         <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
                           xmlns:abc="http://localhost/testapi">
            <soapenv:Header>
               <wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"
                              xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"
                              soapenv:mustUnderstand="1">
                  <wsse:UsernameToken>
                     <wsse:Username>$1</wsse:Username>
                     <wsse:Password Type="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0#PasswordText">$2</wsse:Password>
                  </wsse:UsernameToken>
               </wsse:Security>
            </soapenv:Header>
            <soapenv:Body/>
         </soapenv:Envelope>
      </format>
           <args>
<arg expression="get-property('registry','conf:/users@username')"/>
<arg expression="get-property('registry','conf:/users@password')"/>
</args>
           </payloadFactory>
   <enrich>
      <source type="property" clone="true" property="ORIGINAL_BODY"/>
      <target type="body"/>
   </enrich>
   <log level="full"/>
</sequence>

2. Mediation extension is uploaded during the api creation in publisher in flow.

3. Invoke API endpoint with authorization bearer token provided by WSO2 APIM via SOAP UI.

Reference :

[1] https://docs.oracle.com/cd/E21455_01/common/tutorials/authn_ws_user.html
[2] http://geethwrites.blogspot.com/2014/01/wso2-esb-removing-full-soap-header.html
[3] http://isharapremadasa.blogspot.com/2014/08/wso2-esb-how-to-read-local-entries-and.html

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