Call stored procedure of CosmosDB from API Management Service - azure

Question

I would like for one of my APIs in the API Management Service to call a stored procedure in CosmosDB and return its result. It seems there is not much documentation around the subject.
My attempt so far :
Frontend : GET method with three parameters
Inbound processing : I adapted the code from this question as follows
<policies>
<inbound>
<base />
<set-variable name="Content-Type" value="application/query+json" />
<set-variable name="x-ms-documentdb-isquery" value="True" />
<set-variable name="x-ms-documentdb-query-enablecrosspartition" value="False" />
<set-variable name="x-ms-max-item-count" value="1000" />
<set-variable name="x-ms-version" value="2017-02-22" />
<set-variable name="x-ms-date" value="#( DateTime.UtcNow.ToString("R") )" />
<set-header name="Content-Type" exists-action="override">
<value>#((string)context.Variables["Content-Type"])</value>
</set-header>
<set-header name="x-ms-documentdb-isquery" exists-action="override">
<value>#((string)context.Variables["x-ms-documentdb-isquery"])</value>
</set-header>
<set-header name="x-ms-documentdb-query-enablecrosspartition" exists-action="override">
<value>#((string)context.Variables["x-ms-documentdb-query-enablecrosspartition"])</value>
</set-header>
<set-header name="x-ms-max-item-count" exists-action="override">
<value>#((string)context.Variables["x-ms-max-item-count"])</value>
</set-header>
<set-header name="x-ms-version" exists-action="override">
<value>#((string)context.Variables["x-ms-version"])</value>
</set-header>
<set-header name="x-ms-documentdb-partitionkey" exists-action="override">
<value>#("[\""+context.Subscription.Id+"\"]")</value>
</set-header>
<set-header name="x-ms-date" exists-action="override">
<value>#( (string)context.Variables["x-ms-date"] )</value>
</set-header>
<set-variable name="StringToSign" value="#(string.Format("post\nsprocs\ndbs/{myDBName}/colls/{myCollName}\n{0}\n\n", ((string)context.Variables["x-ms-date"]).ToLowerInvariant()))" />
<set-variable name="cosmosreadwritekey" value="{{MyMasterKeyInReadWriteMode}}" />
<set-variable name="SharedKey" value="#{
// https://learn.microsoft.com/en-us/rest/api/documentdb/access-control-on-documentdb-resources#constructkeytoken
System.Security.Cryptography.HMACSHA256 hasher = new System.Security.Cryptography.HMACSHA256(Convert.FromBase64String((string)context.Variables["cosmosreadwritekey"]));
return Convert.ToBase64String(hasher.ComputeHash(System.Text.Encoding.UTF8.GetBytes((string)context.Variables["StringToSign"])));
}" />
<set-variable name="Authorization" value="#(string.Format("type=master&ver=1.0&sig={0}", ((string)context.Variables["SharedKey"]).Replace("&","%26").Replace("+","%2B").Replace("=","%3D")))" />
<set-header name="Authorization" exists-action="override">
<value>#((string)context.Variables["Authorization"])</value>
</set-header>
<set-backend-service base-url="https://{myCosmosName}.documents.azure.com" />
<rewrite-uri template="/dbs/{myDBName}/colls/{myCollName}/sprocs" />
</inbound>
<backend>
<base />
</backend>
<outbound>
<base />
</outbound>
<on-error>
<base />
</on-error>
</policies>
Backend: HTTPS endgoing with the following URL : https://{myCosmosName}.documents.azure.com/
However, when I test the API I systematically get the following error message :
The input authorization token can't serve the request. Please check that the expected payload is built as per the protocol, and check the key being used. Server used the following payload to sign: 'get\nsprocs\ndbs/{myDBName}/colls/{myDBName}\ntue, 18 sep 2018 09:31:58 gmt\n\n'\r\nActivityId: 64586521-cf37-44e5-80a4-bac0a9d3b261, Microsoft.Azure.Documents.Common/2.0.0.0
My questions from there:
How can I make this call work for my stored procedure?
How can I pass the API parameters to the call to the stored procedure?

Answer 1

For sending parameters, take a look at this. It looks like there is something wrong setting Authorization token, refer to this.