diff --git a/frontend/src/lib/components/Navbar.svelte b/frontend/src/lib/components/Navbar.svelte
index af3d981..a295b83 100644
--- a/frontend/src/lib/components/Navbar.svelte
+++ b/frontend/src/lib/components/Navbar.svelte
@@ -35,10 +35,10 @@
 						<span
 							class="grid h-7 w-7 place-items-center rounded-full bg-neutral-700 text-xs font-semibold uppercase"
 						>
-							{(user.name ?? user.email ?? '?').charAt(0)}
+							{user.name.charAt(0)}
 						</span>
 					{/if}
-					<span class="hidden sm:inline">{user.name ?? user.email}</span>
+					<span class="hidden sm:inline">{user.name}</span>
 				</a>
 				<form method="POST" action="/logout">
 					<button
diff --git a/frontend/src/lib/server/auth.ts b/frontend/src/lib/server/auth.ts
index 0dafe1a..551eb66 100644
--- a/frontend/src/lib/server/auth.ts
+++ b/frontend/src/lib/server/auth.ts
@@ -70,17 +70,32 @@ export async function decodeSession(token: string | undefined): Promise<Session
 	}
 }
 
+function claimString(value: unknown): string | undefined {
+	return typeof value === 'string' && value.length > 0 ? value : undefined;
+}
+
+export function toSessionUser(claims: Record<string, unknown>, fallback?: SessionUser): SessionUser {
+	const sub = claimString(claims.sub) ?? fallback?.sub ?? '';
+	return {
+		sub,
+		name:
+			claimString(claims.name) ??
+			claimString(claims.preferred_username) ??
+			fallback?.name ??
+			claimString(claims.email) ??
+			sub,
+		email: claimString(claims.email) ?? fallback?.email ?? '',
+		picture: claimString(claims.picture) ?? fallback?.picture ?? ''
+	};
+}
+
 export async function refreshSession(session: Session): Promise<Session | null> {
 	if (!session.refreshToken) return null;
 	try {
 		const config = await getOidcConfig();
 		const tokens = await client.refreshTokenGrant(config, session.refreshToken);
-		const claims = tokens.claims();
 		return {
-			sub: session.sub,
-			name: (claims?.name as string | undefined) ?? session.name,
-			email: (claims?.email as string | undefined) ?? session.email,
-			picture: (claims?.picture as string | undefined) ?? session.picture,
+			...toSessionUser(tokens.claims() ?? {}, session),
 			accessToken: tokens.access_token,
 			refreshToken: tokens.refresh_token ?? session.refreshToken,
 			idToken: tokens.id_token ?? session.idToken,
diff --git a/frontend/src/lib/types.ts b/frontend/src/lib/types.ts
index ed92d10..bb2191e 100644
--- a/frontend/src/lib/types.ts
+++ b/frontend/src/lib/types.ts
@@ -1,6 +1,6 @@
 export interface SessionUser {
 	sub: string;
-	name?: string;
-	email?: string;
-	picture?: string;
+	name: string;
+	email: string;
+	picture: string;
 }
diff --git a/frontend/src/routes/auth/callback/+server.ts b/frontend/src/routes/auth/callback/+server.ts
index 2928a7b..1a65f23 100644
--- a/frontend/src/routes/auth/callback/+server.ts
+++ b/frontend/src/routes/auth/callback/+server.ts
@@ -5,6 +5,7 @@ import {
 	getOidcConfig,
 	encodeSession,
 	sessionCookieOptions,
+	toSessionUser,
 	type Session,
 	SESSION_COOKIE,
 	STATE_COOKIE,
@@ -44,10 +45,7 @@ export const GET: RequestHandler = async ({ url, cookies }) => {
 	}
 
 	const session: Session = {
-		sub: String(claims.sub),
-		name: claims.name as string | undefined,
-		email: claims.email as string | undefined,
-		picture: claims.picture as string | undefined,
+		...toSessionUser(claims),
 		accessToken: tokens.access_token,
 		refreshToken: tokens.refresh_token,
 		idToken: tokens.id_token,