chore: import upstream snapshot with attribution

examples/provider-http/basic/README.md

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+# provider-http/basic (HTTP Provider Example)
+
+You can run this example with:
+
+```bash
+npx promptfoo@latest init --example provider-http/basic
+cd provider-http/basic
+```
+
+This example demonstrates how to configure and use HTTP providers with promptfoo to integrate with external API endpoints.
+
+## Quick Start
+
+1. Visit the [HTTP Provider Generator](/http-provider-generator) to automatically generate configurations based on your HTTP endpoint.
+2. Enter your request configuration and sample response.
+3. Copy the generated configuration to your promptfoo config file.
+
+## Example Configuration
+
+Here's a basic example configuration for an HTTP provider that sends prompts to an API endpoint:
+
+```yaml
+providers:
+  - id: https://api.example.com/chat
+    config:
+      method: POST
+      headers:
+        Content-Type: application/json
+      body:
+        messages:
+          - role: user
+            content: '{{prompt}}'
+      transformResponse: json.choices[0].message.content
+```
+
+## Configuration Options
+
+- `method`: HTTP method (GET, POST, PUT, etc.)
+- `headers`: Request headers (Content-Type, Authorization, etc.)
+- `body`: Request body (supports template variables like `{{prompt}}`)
+- `queryParams`: URL query parameters
+- `transformResponse`: JavaScript expression to extract the response
+
+## Usage Steps
+
+1. Copy the example configuration above
+2. Modify the configuration for your endpoint:
+   - Update the URL
+   - Adjust headers (add authentication if needed)
+   - Modify the request body structure
+   - Update the transformResponse to match your API's response format
+3. Test the configuration using the [HTTP Provider Generator](/http-provider-generator)
+4. Save the working configuration to your promptfoo config file
+
+## Testing Locally
+
+To test your configuration:
+
+1. Create a promptfooconfig.yaml file with your configuration
+2. Run the evaluation:
+   ```bash
+   promptfoo eval
+   ```
+3. View the results:
+   ```bash
+   promptfoo view
+   ```
+
+For development and testing, you can use services like [webhook.site](https://webhook.site) to create test endpoints.
+
+For more detailed information, see the [HTTP Provider documentation](/docs/providers/http).

examples/provider-http/basic/promptfooconfig.yaml

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+# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
+description: 'HTTP provider test'
+
+prompts:
+  - 'Write a tweet about {{topic}}'
+  - 'Write a very concise, funny tweet about {{topic}}'
+
+providers:
+  - id: https://webhook.site/3d47d2dd-d450-4869-b80d-41862e577e45
+    config:
+      method: 'POST'
+      headers:
+        'Content-Type': 'application/json'
+      body:
+        'prompt': '{{prompt}}'
+        'model':
+          '{{model}}'
+          #
+      # Parse OpenAI response
+      transformResponse: 'json.choices[0].message.content'
+
+tests:
+  - vars:
+      model: gpt-5
+      topic: bananas