adding example policies for tpm and circuit breaker

examples/README.md

@@ -51,3 +51,4 @@ Overview
 | <a href="Extracting multiple values from xml documents.policy.xml">Extract multiple values from xml documents</a>                                                                  | Uses an intermediate json object to provide easy access to extracted values from an xml document.                                                                                                                                     |
 | <a href="Return a blob URL signed with a user delegation SAS token.xml">Return a blob URL signed with a user delegation SAS token</a>                                              | Demonstrates how to check if a blob exists and then return the URL of the blob signed with a User Delegation SAS token leveraging Managed Identity.                                                                                   | 
 | <a href="oauth-proxy/readme.md">OAuth Reverse Proxy</a>                                              | Demonstrates how to implement an OAuth Reverse Proxy to provide OIDC authentication in-front of a Web Application behind Azure API Management.                                                                                   | 
+| <a href="Rate limit by TPM.xml">Rate limit by TPM (Tokens per minute)</a>                                              | Demonstrates how to implement a TPM based rate limiting policy in Azure API Management.                                                                                   | 

examples/Rate limit by TPM.xml

@@ -0,0 +1,30 @@
+
+<policies>
+	<inbound>
+		<base />
+		<!--Priority Management Based on Subscription Keys:
+			Applies quotas based on the subscription key. -->
+		<choose>
+			<when condition="@(context.Subscription.Id == "subscription1")">
+				<!-- Rate limit by TPM 
+				Each subscription has its own TPM counter ('subscription1TPM' in this case) that tracks total tokens used per request. 
+				If the response status is 200, the counter increases by the token count obtained in the response body. 
+				If the counter hits the 500 TPM limit within 60 seconds, the request will not be forwarded to the backend.
+				Clients recieve 429 as the response status code.
+				 -->
+				<rate-limit-by-key calls="500" renewal-period="60" counter-key="@(String.Concat(context.Subscription.Id,"TPM"))" increment-condition="@(context.Response.StatusCode >= 200 && context.Response.StatusCode < 400)" increment-count="@(context.Response.Body.As<JObject>(true).SelectToken("usage.total_tokens").ToObject<int>())" remaining-calls-header-name="remainingTPM" total-calls-header-name="totalTPM" />
+			</when>
+			<when condition="@(context.Subscription.Name == "subscription2")">
+				<!-- Rate limit by TPM -->
+				<rate-limit-by-key calls="200" renewal-period="60" counter-key="@(String.Concat(context.Subscription.Id,"TPM"))" increment-condition="@(context.Response.StatusCode >= 200 && context.Response.StatusCode < 400)" increment-count="@(context.Response.Body.As<JObject>(true).SelectToken("usage.total_tokens").ToObject<int>())" remaining-calls-header-name="remainingTPM" total-calls-header-name="totalTPM" />
+			</when>
+			<otherwise>
+				<rate-limit-by-key calls="5" renewal-period="60" counter-key="@(context.Subscription.Id)" />
+			</otherwise>
+		</choose>
+	</inbound>
+	<backend>
+		<!--The backend section inherits the base behavior without additional policies.-->
+		<base />
+	</backend>
+</policies>