Best Authentication for SvelteKit SaaS in 2026

Strengths

• ✓User and session tables sit in your database, so joins are ordinary SQL.
• ✓Plugin system covers passkeys, two factor and organizations without vendor lock-in.
• ✓Fully typed API surface, so misuse usually shows up at compile time.

Tradeoffs

• ✗You run and patch the auth code yourself, including security updates.
• ✗Login screens are your responsibility, since the library ships logic not UI.
• ✗Younger project, so APIs still move and older guides go stale quickly.

Strengths

• ✓The user table is a Postgres table, so foreign keys to it just work.
• ✓Row level security policies read the session directly, pushing authorization into the database.
• ✓One vendor for auth, storage and database keeps the moving parts low.

Tradeoffs

• ✗Bundled with Supabase, so adopting it usually means adopting the whole platform.
• ✗Auth schema lives in a managed namespace you cannot freely reshape.
• ✗Row level security is powerful but easy to get subtly wrong.

Strengths

• ✓Enormous library of OAuth providers configured with a few lines each.
• ✓Years of production usage mean most errors already have a forum answer.
• ✓Adapters let you keep sessions in whichever database you already chose.

Tradeoffs

• ✗Anything past OAuth, like invitations or roles, you design yourself.
• ✗Callback and adapter APIs have churned across major versions more than once.
• ✗Documentation lags the code, so reading the source becomes routine.

Strengths

• ✓You end up understanding exactly how your session cookies and tokens work.
• ✓Zero dependency to break, deprecate or change licence underneath you.
• ✓Session schema is yours, so it fits whatever data model you already have.

Tradeoffs

• ✗Copied code means you carry the maintenance and security review forever.
• ✗No package upgrades, so fixes only land if you go looking for them.
• ✗Every provider, reset flow and rate limit is hand-rolled work.