Add auth foundation: sessions/tokens schema, Argon2 hashing, config

Two tables (sessions, user_tokens) + migration; only token *hashes* are stored, so a DB leak yields no usable credential. Argon2id password hashing and token primitives in app/core/security. Config and .env.example gain session/cookie/token TTLs, app base URL, and SMTP settings (twelve-factor). Migration verified reversible (drops the token_purpose enum) and matches the models.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/core/config.py

@@ -27,6 +27,22 @@ class Settings(BaseSettings):
         default="postgresql+asyncpg://provenance:provenance@localhost:5432/provenance",
     )
 
+    # --- Auth / sessions ---
+    session_ttl_days: int = 30
+    token_ttl_hours: int = 24  # email-verify / password-reset token lifetime
+    cookie_name: str = "provenance_session"
+    cookie_secure: bool = True  # set false for local http; true behind TLS
+    # Base URL used to build links in outbound email.
+    app_base_url: str = "http://localhost"
+
+    # --- Email (SMTP) ---
+    mailer: str = Field(default="console", description="console | smtp")
+    smtp_host: str | None = None
+    smtp_port: int = 587
+    smtp_username: str | None = None
+    smtp_password: str | None = None
+    smtp_from: str = "Provenance <no-reply@provenance.local>"
+
 
 @lru_cache
 def get_settings() -> Settings:

backend/app/core/security.py

@@ -0,0 +1,35 @@
+"""Password hashing and token primitives.
+
+Passwords use Argon2id (argon2-cffi). Session and email tokens are random
+high-entropy strings; only their SHA-256 hash is stored, so a database leak
+never exposes a usable credential.
+"""
+
+import hashlib
+import secrets
+
+from argon2 import PasswordHasher
+from argon2.exceptions import Argon2Error
+
+_hasher = PasswordHasher()
+
+
+def hash_password(password: str) -> str:
+    return _hasher.hash(password)
+
+
+def verify_password(password_hash: str, password: str) -> bool:
+    try:
+        return _hasher.verify(password_hash, password)
+    except (Argon2Error, ValueError):
+        return False
+
+
+def generate_token() -> str:
+    """A URL-safe, high-entropy token (the raw secret handed to the client)."""
+    return secrets.token_urlsafe(32)
+
+
+def hash_token(token: str) -> str:
+    """SHA-256 of a token — what we store and look up by."""
+    return hashlib.sha256(token.encode("utf-8")).hexdigest()