Add full support for OIDC prompt=create

[axies20]

Description

Open.IdentityServer 1.0.2 defines the standard prompt value:

OidcConstants.PromptModes.Create

However, Constants.SupportedPromptModes does not include it. The collection currently contains only none, login, consent, and select_account.

As a result, an authorization request containing:

prompt=create

is treated as unsupported by AuthorizeRequestValidator and silently ignored. The value is not copied to ValidatedAuthorizeRequest.PromptModes / AuthorizationRequest.PromptModes.

prompt=create is standardized by Initiating User Registration via OpenID Connect and is also exposed by Microsoft.IdentityModel as OpenIdConnectPrompt.Create.

Expected behavior

Open.IdentityServer should provide complete support for prompt=create:

• include OidcConstants.PromptModes.Create in Constants.SupportedPromptModes;
• expose create in discovery metadata via prompt_values_supported;
• make it available through AuthorizationRequest.PromptModes;
• provide a supported interaction mechanism for directing the user to account creation;
• correctly resume the authorization flow after registration;
• include validation and interaction-flow tests.

Additional consideration

Adding Create only to SupportedPromptModes may not be sufficient. AuthorizeInteractionResponseGenerator.ProcessConsentAsync() currently rejects prompt modes other than none and consent after login processing. Since ProcessLoginAsync() does not handle or remove create, a complete implementation likely also needs interaction-generator behavior for this prompt.

Reproduction

1. Configure an OpenID Connect client using Authorization Code flow.
2. Send a valid authorization request with prompt=create.
3. Inspect the resulting authorization context.
4. PromptModes does not contain create, and the normal login interaction is used.

Version

• Open.IdentityServer: 1.0.2
• Package repository commit: 114dd0a798cf09455cee618dd4d35e41fe9049d3

[patchandthat]

Thanks. This is something we'll look to add.