I have a backend API I want to proxy by using Azure API Management. This backend API requires me to provide a Bearer Oauth2 token. I want to use Azure APIM to handle the Oauth2 flows for me, and I want to expose a very simple API that will be consumed by client apps. I want to avoid my client App to use Oauth2. How can I handle it with APIM? I found a lot of samples demonstrating how to protect a backend API with Oauth2, but it is not the use case I'm trying to implement. Thanks.
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2 Answers
Here is a policy snippet to make this work:
<send-request ignore-error="true" timeout="20" response-variable-name="bearerToken" mode="new"> <set-url>{{authorizationServer}}</set-url> <set-method>POST</set-method> <set-header name="Content-Type" exists-action="override"> <value>application/x-www-form-urlencoded</value> </set-header> <set-body> @{ return "client_id={{clientId}}&resource={{scope}}&client_secret={{clientSecret}}&grant_type=client_credentials"; } </set-body> </send-request> <set-header name="Authorization" exists-action="override"> <value> @("Bearer " + (String)((IResponse)context.Variables["bearerToken"]).Body.As<JObject>()["access_token"]) </value> </set-header> <!-- We do not want to expose our APIM subscription key to the backend API --> <set-header exists-action="delete" name="Ocp-Apim-Subscription-Key"/> And on the APIM policy snippets branch from the APIM team https://github.com/Azure/api-management-policy-snippets/blob/master/examples/Get%20OAuth2%20access%20token%20from%20AAD%20and%20forward%20it%20to%20the%20backend.policy.xml
4 Comments
Dibran
Its actually there now: github.com/Azure/api-management-policy-snippets/blob/master/…
Sai
I keep getting internal server error using this policy, "message": "Expression evaluation failed.", "expression": "\"Bearer \" + (String)((IResponse)context.Variables[\"bearerToken\"]).Body.As<JObject>()[\"access_token\"]", "details": "Unexpected character encountered while parsing value: <. Path '', line 0, Please advise
Varesh
How is this an acceptable solution. This is making a additional API call for every request. However, the purpose of the Access Token is that they have expiration and till it is expired, one should not be using a new token. This would not work for a production load setup. Needs caching of the token's, validation of the token expiration and other things. Have Azure team yet not found a proper solution to this? Sorry my frustration is towards Azure, this is very helpful.
What you need to do is add a header to request - use set-header policy to Set Authorization header to a desired value. That would work well if you can hardcode token in policy.
If you cant - the you have to organize OAuth flow inside policy using send-request. In short, what you'll be doing is sending you app id and secret to OAuth endpoint and parsing its response to obtain token and attach it to request.
