1. Why Does an Angular Request Work in Postman but Fail in the Browser?

Main Reason

Because CORS is enforced by browsers, not by tools like Postman.

Example:

Angular
http://localhost:4200
        ↓
Browser applies CORS rules
        ↓
ASP.NET Core
https://localhost:7001

But Postman works like this:

Postman
   ↓
Direct HTTP request
   ↓
ASP.NET Core

Postman does not normally enforce the browser's Same-Origin Policy or CORS restrictions.

So this situation is common:

Postman           → Works
Angular Browser   → CORS error

Example

Angular sends:

this.http.get(
  'https://localhost:7001/api/products'
);

Angular is running from:

http://localhost:4200

The API is running from:

https://localhost:7001

These are different origins.

If ASP.NET Core does not allow:

http://localhost:4200

the browser may block Angular from accessing the response.

Typical Browser Error

You may see:

Access to XMLHttpRequest at
'https://localhost:7001/api/products'
from origin
'http://localhost:4200'
has been blocked by CORS policy.

But the same endpoint may work perfectly in Postman.

That means:

The API itself may be reachable, but the browser is rejecting the cross-origin interaction.

Other Browser-Only Issues

CORS is the most common reason, but browser requests can also fail because of:

• Mixed content: HTTPS page calling an HTTP API
• Invalid/untrusted development certificate
• Cookie SameSite restrictions
• Missing withCredentials
• Preflight failure
• CSP/security headers
• Browser extensions

So:

Works in Postman
≠
API is correctly configured for browser clients

2. What Does AllowAnyOrigin() Do?

Definition

AllowAnyOrigin() tells ASP.NET Core's CORS policy to allow requests from any origin.

Example:

builder.Services.AddCors(options =>
{
    options.AddPolicy(
        "OpenCors",
        policy =>
        {
            policy
                .AllowAnyOrigin()
                .AllowAnyHeader()
                .AllowAnyMethod();
        });
});

Apply it:

app.UseCors("OpenCors");

Now browser JavaScript hosted on many different origins can access the API, subject to the rest of the policy.

Conceptually:

http://localhost:4200
https://site-a.com
https://site-b.com
https://unknown-site.com

         ↓

       API

    All origins
      allowed

Response Header

With unrestricted origins, the server can return:

Access-Control-Allow-Origin: *

The * means:

Any origin

AllowAnyOrigin() vs WithOrigins()

Allow Any Origin

.AllowAnyOrigin()

means:

Any website origin
        ↓
Browser may access API response

Specific Origins

.WithOrigins(
    "https://www.example.com",
    "https://admin.example.com"
)

means:

Only specifically trusted origins
        ↓
Browser may access API response

For a private Angular frontend, the second approach is generally more restrictive.

3. Why Can AllowAnyOrigin() Be Dangerous?

The important point is:

AllowAnyOrigin() doesn't automatically make an API unauthenticated, but it removes an important browser-side restriction on which websites can read responses from the API.

Suppose your API intentionally supports only:

https://www.example.com

But you configure:

.AllowAnyOrigin()

Now JavaScript running from unrelated websites may also be permitted by CORS to make browser requests and read allowed responses.

Example

Suppose the intended architecture is:

Your Angular App
https://www.example.com
        ↓
      API

Ideally:

.WithOrigins(
    "https://www.example.com"
)

But with:

.AllowAnyOrigin()

the CORS policy is effectively open to:

https://www.example.com
https://attacker.example
https://random-site.example
...

That increases your application's browser-accessible attack surface.

Does AllowAnyOrigin() Bypass JWT Authentication?

No.

This is very important.

If your API endpoint has:

[Authorize]

a caller still needs valid authentication.

So:

AllowAnyOrigin()
     ↓
Controls browser origin access

[Authorize]
     ↓
Controls authenticated API access

They are separate concerns.

An attacker cannot simply gain Admin privileges because you used:

.AllowAnyOrigin()

But overly broad CORS can expose API responses to origins that did not need browser access.

Why Use WithOrigins() Instead?

If only your Angular application needs access:

.WithOrigins(
    "https://www.example.com"
)

implements the principle of least privilege.

Instead of:

Allow everyone

you configure:

Allow only applications that need access

AllowAnyOrigin() and Cookies

This is especially important.

ASP.NET Core does not allow the combination:

.AllowAnyOrigin()
.AllowCredentials()

because credentialed cross-origin requests should not be permitted from an unrestricted wildcard origin.

Instead use an explicit origin:

policy
    .WithOrigins(
        "https://www.example.com"
    )
    .AllowCredentials();

For Angular:

this.http.get(url, {
  withCredentials: true
});

Recommended Configuration

For development:

builder.Services.AddCors(options =>
{
    options.AddPolicy(
        "AngularApp",
        policy =>
        {
            policy
                .WithOrigins(
                    "http://localhost:4200"
                )
                .AllowAnyHeader()
                .AllowAnyMethod();
        });
});

For production:

builder.Services.AddCors(options =>
{
    options.AddPolicy(
        "AngularApp",
        policy =>
        {
            policy
                .WithOrigins(
                    "https://www.example.com"
                )
                .AllowAnyHeader()
                .AllowAnyMethod();
        });
});

This is usually preferable to:

.AllowAnyOrigin()

for an API intended only for known frontends.

Common Mistake

Developers sometimes encounter:

CORS error

and fix it by immediately adding:

.AllowAnyOrigin()
.AllowAnyHeader()
.AllowAnyMethod()

It may make the browser request work, but it can be broader than necessary.

A better approach is:

.WithOrigins(
    "http://localhost:4200"
)
.AllowAnyHeader()
.AllowAnyMethod();

Then add additional trusted origins explicitly as needed.

Key Points

• Browsers enforce CORS; Postman generally does not.
• Therefore an API may work in Postman but fail from Angular.
• Angular and the API commonly use different origins during development.
• Browser CORS failures can include failed preflight requests.
• AllowAnyOrigin() permits browser access from any origin under that CORS policy.
• It commonly produces Access-Control-Allow-Origin: *.
• AllowAnyOrigin() does not disable authentication or authorization.
• However, it broadens which websites can interact with and read the API through browser JavaScript.
• For private APIs, prefer explicitly trusted origins using WithOrigins().
• Avoid blindly using AllowAnyOrigin() merely to suppress a CORS error.
• AllowAnyOrigin() cannot be combined with credentialed CORS via AllowCredentials().
• CORS is a browser-access policy, not your primary API security mechanism.

Interview Questions & Answers

1. Why does an API work in Postman but fail in Angular?

Because browsers enforce the Same-Origin Policy and CORS. Postman does not normally enforce browser CORS restrictions.

2. Does a successful Postman request prove that CORS is configured correctly?

No.

It proves that the API can process the HTTP request. CORS is specifically relevant to browser-based cross-origin access.

3. What does AllowAnyOrigin() do?

It allows browser requests from any origin under the configured CORS policy.

.AllowAnyOrigin()

typically corresponds to:

Access-Control-Allow-Origin: *

4. Why can AllowAnyOrigin() be risky?

Because it unnecessarily allows browser JavaScript from any origin to interact with and read permitted API responses. For APIs intended for specific frontends, that violates least-privilege configuration.

5. Does AllowAnyOrigin() allow unauthenticated users through [Authorize]?

No.

CORS and authentication are independent:

CORS
→ Which browser origins?

Authentication
→ Who are you?

Authorization
→ What can you do?

6. What should you use instead of AllowAnyOrigin()?

For a known Angular frontend:

.WithOrigins(
    "https://www.example.com"
)

This permits only the explicitly trusted frontend origin.

7. Can you use AllowAnyOrigin() with AllowCredentials()?

No. Credentialed CORS requires explicitly trusted origins rather than a wildcard origin.

Interview Quick Answer

An Angular request can work in Postman but fail in the browser because CORS is enforced by browsers, while Postman does not normally enforce browser-origin restrictions. AllowAnyOrigin() permits browser access from any origin, typically using Access-Control-Allow-Origin: *. Although it does not bypass JWT authentication, it can be overly permissive, so APIs intended for known Angular clients should normally use WithOrigins() to allow only trusted origins.