diff --git a/.changeset/rare-lamps-worry.md b/.changeset/rare-lamps-worry.md
new file mode 100644
index 000000000..12d84219b
--- /dev/null
+++ b/.changeset/rare-lamps-worry.md
@@ -0,0 +1,9 @@
+---
+"@logto/core": patch
+---
+
+Support comma separated resource parameter
+
+Some third-party libraries or plugins do not support array of resources, and can only specify `resource` through `additionalParameters` config, e.g. `flutter-appauth`. However, only one resource can be specified at a time in this way. This PR enables comma separated resource parameter support in Logto core service, so that multiple resources can be specified via a single string.
+
+For example: Auth URL like `/oidc/auth?resource=https://example.com/api1,https://example.com/api2` will be interpreted and parsed to Logto core service as `/ordc/auth?resource=https://example.com/api1&resource=https://example.com/api2`.
diff --git a/packages/core/src/middleware/koa-resource-param.test.ts b/packages/core/src/middleware/koa-resource-param.test.ts
new file mode 100644
index 000000000..235f8fa03
--- /dev/null
+++ b/packages/core/src/middleware/koa-resource-param.test.ts
@@ -0,0 +1,45 @@
+import createMockContext from '#src/test-utils/jest-koa-mocks/create-mock-context.js';
+
+const { jest } = import.meta;
+
+const { default: koaResourceParam } = await import('./koa-resource-param.js');
+
+// eslint-disable-next-line @typescript-eslint/no-empty-function
+const noop = async () => {};
+
+const endpoint = 'https://logto.io/oidc/auth';
+
+describe('koaResourceParam() middleware', () => {
+  it('should check and process comma separated resource params in the URL', async () => {
+    const ctx = createMockContext({ url: endpoint + '?resource=foo,bar' });
+    const run = koaResourceParam();
+
+    await run(ctx, noop);
+
+    expect(ctx.request.query).toEqual({
+      resource: ['foo', 'bar'],
+    });
+  });
+
+  it('should also work with both comma separated and single resource params', async () => {
+    const ctx = createMockContext({ url: endpoint + '?resource=foo,bar&resource=baz' });
+    const run = koaResourceParam();
+
+    await run(ctx, noop);
+
+    expect(ctx.request.query).toEqual({
+      resource: ['foo', 'bar', 'baz'],
+    });
+  });
+
+  it('should not affect the URL if no comma separated resource params are found', async () => {
+    const ctx = createMockContext({ url: endpoint + '?resource=foo&resource=bar' });
+    const run = koaResourceParam();
+
+    await run(ctx, noop);
+
+    expect(ctx.request.query).toEqual({
+      resource: ['foo', 'bar'],
+    });
+  });
+});
diff --git a/packages/core/src/middleware/koa-resource-param.ts b/packages/core/src/middleware/koa-resource-param.ts
new file mode 100644
index 000000000..8728407df
--- /dev/null
+++ b/packages/core/src/middleware/koa-resource-param.ts
@@ -0,0 +1,31 @@
+import type { Nullable } from '@silverhand/essentials';
+import type { MiddlewareType } from 'koa';
+
+/**
+ * Create a middleware function that checks if the request URL contains comma separated `resource` query parameter.
+ * If yes, split the values and reconstruct the URL with multiple `resource` query parameters.
+ * E.g. `?resource=foo,bar` => `?resource=foo&resource=bar`
+ */
+export default function koaResourceParam<StateT, ContextT, ResponseBodyT>(): MiddlewareType<
+  StateT,
+  ContextT,
+  Nullable<ResponseBodyT>
+> {
+  return async (ctx, next) => {
+    const { query } = ctx.request;
+    const { resource } = query;
+
+    if (!resource) {
+      return next();
+    }
+
+    const resources = Array.isArray(resource) ? resource : [resource];
+    const resourceParams = resources.flatMap((resource) => resource.split(','));
+
+    ctx.request.query = {
+      ...query,
+      resource: resourceParams,
+    };
+    return next();
+  };
+}
diff --git a/packages/core/src/oidc/init.ts b/packages/core/src/oidc/init.ts
index 4d9ff4d7c..769985d15 100644
--- a/packages/core/src/oidc/init.ts
+++ b/packages/core/src/oidc/init.ts
@@ -28,6 +28,7 @@ import { type CloudConnectionLibrary } from '#src/libraries/cloud-connection.js'
 import { type LogtoConfigLibrary } from '#src/libraries/logto-config.js';
 import koaAuditLog from '#src/middleware/koa-audit-log.js';
 import koaBodyEtag from '#src/middleware/koa-body-etag.js';
+import koaResourceParam from '#src/middleware/koa-resource-param.js';
 import postgresAdapter from '#src/oidc/adapter.js';
 import {
   buildLoginPromptUrl,
@@ -377,6 +378,12 @@ export default function initOidc(
       throw error;
     }
   });
+  /**
+   * Check if the request URL contains comma separated `resource` query parameter. If yes, split the values and
+   * reconstruct the URL with multiple `resource` query parameters.
+   * E.g. `?resource=foo,bar` => `?resource=foo&resource=bar`
+   */
+  oidc.use(koaResourceParam());
   /**
    * `oidc-provider` [strictly checks](https://github.com/panva/node-oidc-provider/blob/6a0bcbcd35ed3e6179e81f0ab97a45f5e4e58f48/lib/shared/selective_body.js#L11)
    * the `content-type` header for further processing.