title: How to start Azure B2C User Flows from Blazor WASM application using MSAL 2
body: <p>I've successfully configured the <strong>Azure B2C</strong> service so that a <strong>Blazor WASM</strong> application will launch my B2C_1_Signin User Flow by navigating to <code>/authentication/login</code> in my application.</p>
  <p>Now, I'm trying to launch my B2C_1_Signup User Flow. When I try <code>/authentication/register</code>, I get a message saying that <em>Registration is not supported</em>. I assume I am missing some configuration, but I can't find any documentation on how to proceed.</p>
  <p>Here's what I've tried:</p>
  <ol>
  <li>In my wwwroot/appsettings.json, I've tried adding settings to tell MSAL what User Flows to use:</li>
  </ol>
  <pre><code>{
    &quot;AzureAdB2C&quot;: {
      &quot;Authority&quot;: &quot;https://xxx/yyy/B2C_1_Signin&quot;,
      &quot;ClientId&quot;: &quot;0000-0000-0000&quot;,
      &quot;ValidateAuthority&quot;: false,
      &quot;SignUpPolicyId&quot;: &quot;B2C_1_Signup&quot;,
      &quot;SignInPolicyId&quot;: &quot;B2C_1_Signin&quot;
    }
  }
  </code></pre>
  <p>...but this doesn't work.</p>
  <ol start="2">
  <li>I crawled through the <code>Microsoft.AspNetCore.Components.WebAssembly.Authentication</code> source code until I found the <em>Registration is not supported</em> message. Based on the surrounding code, it looks like it is expecting a value in <code>RemoteRegisterPath</code>, so I modified my Program.cs as follows:</li>
  </ol>
  <pre><code>builder.Services.AddMsalAuthentication(options =&gt;
  {
      builder.Configuration.Bind(&quot;AzureAdB2C&quot;, options.ProviderOptions.Authentication);
      options.ProviderOptions.DefaultAccessTokenScopes.Add(&quot;openid&quot;);
      options.ProviderOptions.DefaultAccessTokenScopes.Add(&quot;offline_access&quot;);
      options.ProviderOptions.LoginMode = &quot;redirect&quot;;
  
      options.AuthenticationPaths.RemoteRegisterPath = &quot;https://xxx/yyy/B2C_1_Signup&quot;;
  });
  </code></pre>
  <p>Doing this launches the User Flow, but it seems to need the <strong>full URL</strong> from the Azure B2C site:</p>
  <pre><code>https://xxx/yyy/oauth2/v2.0/authorize?p=B2C_1_Signup&amp;client_id=0000-0000-0000&amp;nonce=defaultNonce&amp;redirect_uri=https%3A%2F%2Flocalhost%3A5001%2Fauthentication%2Flogin-callback&amp;scope=openid&amp;response_type=code&amp;prompt=login&amp;code_challenge_method=S256&amp;code_challenge=F1ut2KaRX...
  </code></pre>
  <p>Since I don't want to handle the full PKCE exchange (e.g. - create the <code>code_challenge</code> and handle the returned <code>code</code>), I'm wondering how to proceed.</p>