APIM policy to get the token and send request in backend

   <backend>

        <retry condition="@(context.Response.StatusCode == 401)" count="2" interval="1" first-fast-retry="true">

            <choose>

                <when condition="@(context.Variables.GetValueOrDefault("calledOnce", false))">

                    <cache-remove-value key="token" />

                </when>

            </choose>

            <!-- Get token -->

            <cache-lookup-value key="token" default-value="noToken" variable-name="token" />

            <!-- Retrieve token if needed -->

            <choose>

                <when condition="@((string)context.Variables["token"] == "noToken")">

                    <set-variable name="clientSecret" value="@(System.Net.WebUtility.UrlEncode("{{concur-clientsecret}}"))" />

                    <!-- Retrieve token -->

                    <send-request ignore-error="false" timeout="20" response-variable-name="tokenResponse" mode="new">

                        <set-url>@($"{{concur-url}}/oauth2/v0/token")</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>@($"grant_type=refresh_token&client_id={{concur-clientid}}&client_secret={(string)context.Variables["clientSecret"]}&refresh_token={{concur-refresh-token}}")</set-body>

                    </send-request>

                    <!-- Cache token -->

                    <set-variable name="response" value="@(((IResponse)context.Variables["tokenResponse"]).Body.As<JObject>())" />

                    <set-variable name="token" value="@(((JObject)context.Variables["response"])["access_token"].ToString())" />

                    <set-variable name="duration" value="@(((JObject)context.Variables["response"])["expires_in"].ToString())" />

                    <cache-store-value key="token" value="@((string)context.Variables["token"])" duration="@(Int32.Parse((string)context.Variables["duration"]))" />

                </when>

            </choose>

            <!-- Use token for authorization

            <set-backend-service base-url="{{concur-url}}/api/v3.0/expense/reports?approvalStatusCode=A_APPR&amp;processingPaymentDateAfter=2024-09-10T04:59:33&amp;processingPaymentDateBefore=2024-10-01T10:57:37&amp;limit=100&amp;user=ALL" />

           -->

            <set-backend-service base-url="{{concur-url}}" />

            <set-header name="Authorization" exists-action="override">

                <value>@("Bearer " + context.Variables["token"])</value>

            </set-header>

            <set-header name="Content-Type" exists-action="override">

                <value>application/json</value>

            </set-header>

            <set-header name="Accept" exists-action="override">

                <value>application/json</value>

            </set-header>

            <set-variable name="calledOnce" value="@(true)" />

            <forward-request buffer-request-body="true" />

        </retry>

    </backend>

APIM Policy to send Data to servicebus managed identity

 <!--

    - Policies are applied in the order they appear.

    - Position <base/> inside a section to inherit policies from the outer scope.

    - Comments within policies are not preserved.

-->

<!-- Add policies as children to the <inbound>, <outbound>, <backend>, and <on-error> elements -->

<policies>

    <!-- Throttle, authorize, validate, cache, or transform the requests -->

    <inbound>

        <base />        

        <authentication-managed-identity resource="https://servicebus.azure.net/" output-token-variable-name="msi-access-token" ignore-error="false" />

        <set-backend-service base-url="https://myservicebus.servicebus.windows.net/" />        

        <rewrite-uri template="salesorder/messages" />

        <set-header name="Content-Type" exists-action="override">

            <value>vnd.microsoft.servicebus.yml</value>

        </set-header>

        <set-header name="Authorization" exists-action="override">

            <value>@("Bearer " + (string)context.Variables["msi-access-token"])</value>

        </set-header>

        <set-body>@{

                JObject json = context.Request.Body.As<JObject>(preserveContent: true);

                return JsonConvert.SerializeObject(json);

            }</set-body>

    </inbound>

    <!-- Control if and how the requests are forwarded to services  -->

    <backend>

        <base />

    </backend>

    <!-- Customize the responses -->

    <outbound>

        <base />

    </outbound>

    <!-- Handle exceptions and customize error responses  -->

    <on-error>

        <base />

    </on-error>

</policies>