Support prompt=create

Allows RPs to ask for account creation

See https://openid.net/specs/openid-connect-prompt-create-1_0.html

crates/oauth2-types/src/oidc.rs

@@ -25,7 +25,7 @@ use serde::Serialize;
 use serde_with::skip_serializing_none;
 use url::Url;
 
-use crate::requests::{Display, GrantType, ResponseMode};
+use crate::requests::{Display, GrantType, Prompt, ResponseMode};
 
 #[derive(Serialize, Clone, Copy, PartialEq, Eq, Hash, Debug)]
 #[serde(rename_all = "lowercase")]
@@ -234,4 +234,7 @@ pub struct Metadata {
     /// Indicates whether the authorization server accepts authorization
     /// requests only via PAR.
     pub require_pushed_authorization_requests: Option<bool>,
+
+    /// Array containing the list of prompt values that this OP supports.
+    pub prompt_values_supported: Option<HashSet<Prompt>>,
 }

crates/oauth2-types/src/requests.rs

@@ -95,6 +95,7 @@ pub enum Prompt {
     Login,
     Consent,
     SelectAccount,
+    Create,
 }
 
 #[serde_as]