add info on how to override auth scheme in generators.yml

Author: devalog

fern/products/api-def/openapi-pages/auth.mdx

@@ -193,4 +193,47 @@ components:
       type: apiKey
       in: header
       name: X_API_KEY   
-```
+```
+
+## Override security scheme
+
+You can use `generators.yml` to define custom authentication schemes that will take precedence when generating SDKs. 
+
+First, use the `auth-schemes` property to define your authentication scheme. Then, specify your auth scheme in the `api` property to override your OpenAPI spec. 
+
+```yml title="generators.yml" {1-6, 8}
+auth-schemes:                 # Define custom auth scheme
+  Bearer:                     
+    scheme: bearer
+    token:
+      name: apiKey             # Custom parameter name in the SDK
+      env: YOUR_TOKEN_NAME     # Environment variable to auto-scan
+api:
+  auth: Bearer # Apply the custom scheme, overriding the OpenAPI spec
+```
+
+### Auth scheme reference
+
+<AccordionGroup>
+<Accordion title="Header authentication">
+<Markdown src="/products/sdks/snippets/header-auth-params.mdx" />
+</Accordion>
+<Accordion title="Basic authentication">
+<Markdown src="/products/sdks/snippets/basic-auth-params.mdx" />
+</Accordion>
+<Accordion title="Bearer token authentication">
+<Markdown src="/products/sdks/snippets/bearer-auth-params.mdx" />
+</Accordion>
+<Accordion title="OAuth authentication">
+<Markdown src="/products/sdks/snippets/oauth-params.mdx" />
+
+#### get-token
+
+<Markdown src="/products/sdks/snippets/oauth-get-token.mdx" />
+
+#### refresh-token
+
+<Markdown src="/products/sdks/snippets/oauth-refresh-token.mdx" />
+</Accordion>
+</AccordionGroup>
+