feat: Implement support for prompt=create in the authorization code flow

src/service/oauth/grant.rs

@@ -18,6 +18,8 @@ pub struct AuthorizationCodeQuery {
 	pub response_mode: ResponseMode,
 	pub code_challenge: String,
 	pub code_challenge_method: CodeChallengeMethod,
+	#[serde(default)]
+	pub prompt: Option<Prompt>,
 }
 
 #[derive(Debug, Clone, Default, Deserialize, Serialize)]
@@ -36,6 +38,15 @@ pub enum CodeChallengeMethod {
 	S256,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(rename_all = "snake_case")]
+#[non_exhaustive]
+pub enum Prompt {
+	Create,
+	#[serde(other)]
+	Unknown,
+}
+
 #[derive(Debug, Clone, Deserialize, Serialize, PartialOrd, Ord)]
 pub enum Scope {
 	Device(OwnedDeviceId),

src/service/users/mod.rs

@@ -245,6 +245,7 @@ impl Service {
 
 			let suffix = &self.services.config.new_user_displayname_suffix;
 			if !suffix.is_empty() {
+				displayname.push(' ');
 				displayname.push_str(suffix);
 			}