Cannot use Blazor WebAssembly debugging with OpenID Connect login due to unpredictable localhost port

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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Summary:

When debugging a Blazor WebAssembly app in Visual Studio with OpenID Connect login (e.g., using OpenIddict), the application is launched on a random localhost port (e.g., https://localhost:51783). This makes it impossible to pre-register a redirect URI for login flows, which are required to match exactly by identity providers.

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Expected behavior:

I expect to be able to:

• Debug my Blazor WebAssembly app normally
• Use OpenID Connect login
• Register a known, stable redirect URI in the identity provider (e.g., https://localhost:5005/authentication/callback)

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Actual behavior:

Blazor WASM debugging launches the app on a random port with each run, like:

https://localhost:51783/

This breaks the OpenID Connect flow because:

• The identity provider requires a static, pre-registered redirect_uri
• The app’s real port is not known until the browser opens

As a result, login fails with invalid_redirect_uri or requires unsafe workarounds like wildcard redirects (which most providers disallow or OpenIddict refuses to match).

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Why this matters:

• Secure login flows (e.g., using OpenIddict, Duende, Auth0) require strict redirect URI matching
• Random ports make reliable debugging impossible
• There is no current way to fix the debug port for Blazor WASM apps in Visual Studio

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Workarounds attempted:

• Tried to use launchSettings.json to fix the port → ignored by Visual Studio for Blazor WASM
• Tried dynamic redirect URI patching → doesn't help since identity provider also requires known redirect_uri
• Tried IHttpContextAccessor or OpenIddictClientService tricks → adds too much complexity

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Repro steps:

1. Create a Blazor WASM project with OpenId Connect login (using OpenIddict or any OIDC provider)
2. Launch in debug mode (F5)
3. Observe that the app uses a random port
4. Attempt login — you'll see a failure due to redirect_uri mismatch

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Suggestion:

Please allow Blazor WebAssembly apps to:

• Set a fixed HTTPS port (via launchSettings.json or Aspire config)
• Or reuse the same debug port across runs
• Or expose the actual launch port to the app before startup

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Original Comments

Feedback Bot on 5/9/2025, 05:17 AM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

[javiercn]

Thanks for contacting us.

@thaystg is this the case for a brand-new app? I don't believe the port changes when we launch under debugging, but I might be wrong?

[octavian-cacina-gotomaxx]

is this the case for a brand-new app? I don't believe the port changes when we launch under debugging, but I might be wrong?

Yes, this is still the case with a brand-new app. The port changes on each launch.