Create openapi.md

doc/dev_guide/openapi.md

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+# OpenAPI
+
+The OpenAPI import feature was failing when trying to import specifications from URLs like https://catfact.ninja/docs?api-docs.json. The error "The fetched content does not look like a valid OpenAPI spec (JSON or YAML)" was shown even though the content was a valid OpenAPI 3.0 specification. This was caused by a bug in the openapi_spec package (v0.15.0) that cannot parse OpenAPI specs containing "security": [[]] (empty security arrays), which is valid according to the OpenAPI 3.0 specification.
+
+> Fix
+
+Added a workaround in OpenApiImportService.tryParseSpec() that detects parsing failures and automatically removes problematic security fields containing empty arrays before retrying the parse operation. This is a temporary workaround until the upstream package is fixed.
+
+- [APIDash](https://drive.google.com/file/d/1CWocxCVW99-bEWkZlwInGq0JykHalv9a/view?usp=sharing) - Works without any fix
+- [Cat Fact API](https://drive.google.com/file/d/1ox71b3tT4Lv-9jw7zV1ronWQR_uW3K25/view?usp=drive_link) - Works with this fix
+- [DigitalOcean Droplet Metadata API](https://drive.google.com/file/d/1XKZXJvrwvAVm3OVBEZFhScOuCMjPJBZh/view?usp=drive_link) - Works without any fix
+- [GitHub v3 REST API](https://drive.google.com/file/d/1WcJXSosHPD0uiybJrqpJSknM5FA0De02/view?usp=drive_link) - Doesn't Work
+- [Swagger Petstore](https://drive.google.com/file/d/1LBqBrlcsXo7Clr7VKn7CYe75c_H4U8zQ/view?usp=drive_link) - Doesn't Work
+- [RailwayStations REST API](https://drive.google.com/file/d/1jVFk-hNf_gb_VeBuAomOgh6tWByU9Fyi/view?usp=drive_link) - Doesn't Work
+- [UniProt REST API Server](https://drive.google.com/file/d/1KTIqKC7SludxsyCYN6kXWQySve4GpbhD/view?usp=drive_link) - Doesn't Work
+- [VIT-AP VTOP API](https://drive.google.com/file/d/1B5Mh3IK2uUBoRSocEKQd2Dvf7SZWm03M/view?usp=drive_link) - Works without any fix
+
+It’s not our parser that causes the issue. The failures come from the documents themselves and how the openapi_spec package (correctly) enforces OpenAPI shapes. Valid security fields work fine as per the package docs; the broken cases are due to invalid spec content.
+
+### Findings per document
+
+- cat_facts.json (also the Cat Facts URL)
+
+  - Problem: Top-level security is malformed: security: [[]]
+  - Why it fails: In OpenAPI 3.0, top-level security must be an array of SecurityRequirement objects (maps). Examples:
+    - Valid: security: [] (no requirements) or security: [ { api_key: [] } ]
+    - Invalid: security: [[]] (array of arrays)
+  - openapi_spec error: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'
+  - Conclusion: The document is invalid. This is not a general “security field” issue, just this malformed shape.
+
+- railway-stations.yaml
+
+  - Problem: Component parameter reference points to a Parameter missing required fields (e.g., 'in').
+  - Error: CheckedFromJsonException: Could not create Parameter. There is a problem with "in". Invalid union type "null"!
+  - The stack/message points at $ref: #/components/parameters/Authorization.
+  - Conclusion: Not related to security. The referenced Parameter definition is incomplete (missing in: header|query|path|cookie) or otherwise invalid.
+
+- travel.yaml
+
+  - Problem: Same class of failure as railway-stations.yaml, with a parameter ref like $ref: #/components/parameters/page.
+  - Error: CheckedFromJsonException... problem with "in" (Invalid union type "null").
+  - Note: components.securitySchemes is present here and is not the cause.
+  - Conclusion: Also a spec issue with parameter component definitions/references.
+
+- digitalocean.yaml
+  - Result: Parses successfully with openapi_spec.
+  - Note: No top-level security; nothing problematic here.
+  - Conclusion: Confirms the parser handles valid documents correctly.
+
+Steps to reproduce failures from local files,
+
+```
+import 'dart:io';
+import 'package:openapi_spec/openapi_spec.dart';
+
+void main(List<String> args) async {
+
+  // Pass file paths as args below.
+  final paths = args.isNotEmpty
+      ? args
+      : <String>[
+          './cat_facts.json',
+          './railway-stations.yaml',
+        ];
+
+  for (final p in paths) {
+    stdout.writeln('\n=== Parsing: $p ===');
+    final f = File(p);
+    if (!await f.exists()) {
+      stdout.writeln('Skip: file not found');
+      continue;
+    }
+
+    final content = await f.readAsString();
+
+    try {
+      final spec = OpenApi.fromString(source: content, format: null);
+      stdout.writeln('SUCCESS: title="${spec.info.title}", version="${spec.info.version}"');
+      stdout.writeln('Paths: ${spec.paths?.length ?? 0}');
+    } catch (e, st) {
+      final err = e.toString();
+      stdout.writeln('FAIL: ${err.substring(0, err.length.clamp(0, 400))}...');
+      // Stack Trace
+      final stStr = st.toString();
+      if (stStr.isNotEmpty) {
+        stdout.writeln('Stack:\n$stStr');
+      }
+    }
+  }
+}
+```
+
+### How to run
+
+- Create a new dart project, put the openapi spec file and this script there.
+- Add the depndency, `dart pub add openapi_spec: ^0.15.0`
+- Run:
+  - `dart run path/to/this/file`
+
+### Expected outcomes
+
+- `cat_facts.json`
+
+  - FAIL with an error like:
+    - type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'
+  - This is triggered by the invalid top-level security shape: security: [[]]
+
+- `railway-stations.yaml`
+  - FAIL with an error like:
+    - CheckedFromJsonException: Could not create `Parameter`. There is a problem with "in". Invalid union type "null"!
+  - This points to a components/parameters reference missing required “in”.