#### [Abblix\.SecurityEvents](https://www.abblix.com/en/docs/api/abblix-securityevents 'index')
### [Abblix\.SecurityEvents\.BackChannelLogout\.Steps](https://www.abblix.com/en/docs/api/abblix-securityevents/Abblix.SecurityEvents.BackChannelLogout.Steps 'Abblix\.SecurityEvents\.BackChannelLogout\.Steps')

## ForbidNonceStep Class

Refuses a Logout Token that carries a `nonce` \- step 7 of OpenID Connect Back\-Channel
Logout 1\.0 Section 2\.6\.

```csharp
public sealed class ForbidNonceStep : Abblix.SecurityEvents.Validation.ISecurityEventTokenValidator
```

Inheritance [System\.Object](https://learn.microsoft.com/en-us/dotnet/api/system.object 'System\.Object') → ForbidNonceStep

Implements [ISecurityEventTokenValidator](https://www.abblix.com/en/docs/api/abblix-securityevents/Abblix.SecurityEvents.Validation.ISecurityEventTokenValidator 'Abblix\.SecurityEvents\.Validation\.ISecurityEventTokenValidator')

### Remarks
The prohibition protects the other endpoint, not this one\. Section 2\.4 says why the claim is
banned: a nonce "is prohibited to make a Logout Token syntactically invalid if used in a forged
Authentication Response in place of an ID Token"\. So refusing it here is this receiver keeping
its half of an agreement that guards the authorization callback \- which is also why the check
belongs in every deployment and not only in those worried about their own logout endpoint\.

Checked before the signature, on the member's presence, because a malformed nonce marks the
token exactly as a well-formed one does and a rejection this cheap should not cost a signature
verification.
### Methods

## ForbidNonceStep\.ValidateAsync\(SecurityEventTokenValidationContext, CancellationToken\) Method {#Abblix.SecurityEvents.BackChannelLogout.Steps.ForbidNonceStep.ValidateAsync(Abblix.SecurityEvents.Validation.SecurityEventTokenValidationContext,System.Threading.CancellationToken)}

Checks the token in flight\.

```csharp
public System.Threading.Tasks.ValueTask<Abblix.SecurityEvents.Validation.SecurityEventTokenValidationError?> ValidateAsync(Abblix.SecurityEvents.Validation.SecurityEventTokenValidationContext context, System.Threading.CancellationToken cancellationToken);
```
#### Parameters

###### `context` [SecurityEventTokenValidationContext](https://www.abblix.com/en/docs/api/abblix-securityevents/Abblix.SecurityEvents.Validation.SecurityEventTokenValidationContext 'Abblix\.SecurityEvents\.Validation\.SecurityEventTokenValidationContext') {#Abblix.SecurityEvents.BackChannelLogout.Steps.ForbidNonceStep.ValidateAsync(Abblix.SecurityEvents.Validation.SecurityEventTokenValidationContext,System.Threading.CancellationToken).context}

The state accumulated by earlier steps\.

###### `cancellationToken` [System\.Threading\.CancellationToken](https://learn.microsoft.com/en-us/dotnet/api/system.threading.cancellationtoken 'System\.Threading\.CancellationToken') {#Abblix.SecurityEvents.BackChannelLogout.Steps.ForbidNonceStep.ValidateAsync(Abblix.SecurityEvents.Validation.SecurityEventTokenValidationContext,System.Threading.CancellationToken).cancellationToken}

Cancels I/O the step performs, such as key retrieval\.

Implements [ValidateAsync\(SecurityEventTokenValidationContext, CancellationToken\)](https://www.abblix.com/en/docs/api/abblix-securityevents/Abblix.SecurityEvents.Validation.ISecurityEventTokenValidator#Abblix.SecurityEvents.Validation.ISecurityEventTokenValidator.ValidateAsync(Abblix.SecurityEvents.Validation.SecurityEventTokenValidationContext,System.Threading.CancellationToken) 'Abblix\.SecurityEvents\.Validation\.ISecurityEventTokenValidator\.ValidateAsync\(Abblix\.SecurityEvents\.Validation\.SecurityEventTokenValidationContext, System\.Threading\.CancellationToken\)')

#### Returns
[System\.Threading\.Tasks\.ValueTask&lt;](https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.valuetask-1 'System\.Threading\.Tasks\.ValueTask\`1')[SecurityEventTokenValidationError](https://www.abblix.com/en/docs/api/abblix-securityevents/Abblix.SecurityEvents.Validation.SecurityEventTokenValidationError 'Abblix\.SecurityEvents\.Validation\.SecurityEventTokenValidationError')[&gt;](https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.valuetask-1 'System\.Threading\.Tasks\.ValueTask\`1')  
Null to pass the token on; an error to stop the pipeline with that verdict\.