Merge pull request #8386 from BLasan/sequence-as-backend

[Doc]: Sequence as a Backend for REST APIs

en/docs/tutorials/create-and-publish-a-sequencebackend-api.md

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+# Create and Publish an API with Sequence as a Backend
+
+When using a sequence as a backend, you can execute any mediation logic which acts as a backend to the **REST API**.
+WSO2 API Manager has integrated the support for invoking **REST API** with custom mediation logic through WSO2 API Gateway. Follow the steps below to create and publish an API with Sequence as a Backend.
+
+## Step 1 - Create a REST API
+
+1. Sign in to the API Publisher Portal `https://<hostname>:9443/publisher`.
+
+2. Click **CREATE API** and then click **Start From Scrach**.
+
+    [![Create a new REST API]({{base_path}}/assets/img/learn/create-lambda-api.png)]({{base_path}}/assets/img/learn/create-lambda-api.png)
+
+3. Enter the API details without an endpoint URL and click **Create**.  
+
+    [![Create a test API]({{base_path}}/assets/img/learn/create-sequence-backend-api.png)]({{base_path}}/assets/img/learn/create-sequence-backend-api.png)
+
+## Step 2 - Add Sequence Backend Endpoint
+
+1. Click **Endpoints** to navigate to Endpoints page.
+
+2. Navigate to the **Sequence Backend Endpoint** type and click **ADD**.
+
+    [![Select Sequence Backend endpoint]({{base_path}}/assets/img/learn/endpoint-select-sequence-backend-endpoint.png)]({{base_path}}/assets/img/learn/endpoint-select-sequence-backend-endpoint.png)
+
+    You will be redirected to the sequence backend page.
+    [![Select Sequence Backend endpoint page]({{base_path}}/assets/img/learn/endpoint-sequence-backend-page.png)]({{base_path}}/assets/img/learn/endpoint-sequence-backend-page.png)
+
+3. Upload a sequence file to the preferred **Key Type**
+
+    To upload, you can hit Add button under the selected key type.
+    Sequence Backend endpoint configuration needs to have atleast one sequence for the API (either SANDBOX or PRODUCTION).
+        [![Upload Sequence Backend]({{base_path}}/assets/img/learn/upload-sequence-backend-file.png)]({{base_path}}/assets/img/learn/upload-sequence-backend-file.png)
+
+    !!!note
+        In both key types, only one sequence is allowed to be added. If a developer wants to replace, then the uploaded one should be deleted from the preferred key type.
+
+4. Click **Save**
+    [![Save the Sequence Uploaded]({{base_path}}/assets/img/learn/endpoint-sequence-backend-save.png)]({{base_path}}/assets/img/learn/endpoint-sequence-backend-save.png)
+
+    This lists the uploaded sequences for the preferred key types.
+    [![List Sequence Backends Uploaded]({{base_path}}/assets/img/learn/list-sequence-backends-uploaded.png)]({{base_path}}/assets/img/learn/list-sequence-backends-uploaded.png)
+
+
+4. Download sequence uploaded of the preferred key type. This will download the sequence uploaded by the user.
+    [![Download Sequence Backend]({{base_path}}/assets/img/learn/sequence-backend-operations.png)]({{base_path}}/assets/img/learn/sequence-backend-operations.png)
+
+5. Delete sequence uploaded from the preferred key type
+    If there's only one item to be deleted, you will not be permitted to perform the operation as atleast one sequence should be provided under the "Sequence Backend" endpoint type.
+
+6. Click **Save**.
+
+    [![Save the Endpoint Configuration]({{base_path}}/assets/img/learn/endpoint-config-sequence-backend-save.png)]({{base_path}}/assets/img/learn/endpoint-config-sequence-backend-save.png)
+
+    !!!note
+         Button will not be enabled if there's no sequence provided under the Sequence Backend endpoint configuration.
+
+!!!note
+        Sequence Backend endpoint type only applicable for REST APIs and can be deployed only in Synapse Gateway.