fix(oidc): missing content type header on openId configuration endpoint

Author: Bekacru

packages/better-auth/src/plugins/oidc-provider/index.ts

@@ -145,7 +145,7 @@ export const oidcProvider = (options: OIDCOptions) => {
 				},
 				async (ctx) => {
 					const metadata = getMetadata(ctx, options);
-					return metadata;
+					return ctx.json(metadata);
 				},
 			),
 			oAuth2authorize: createAuthEndpoint(