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Enhance OAuth security, PKCE, and state validation

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- Enforced stricter PKCE requirements by rejecting insecure 'plain' method for public clients.
- Transitioned client secret hashing to bcrypt for improved security and migration compatibility.
- Added constant-time comparison for state parameter validation to prevent timing attacks.
- Improved error handling and logging for OAuth workflows, including malformed headers and invalid scopes.
- Upgraded Google OIDC token validation to verify both signature and nonce.
- Refactored OAuth service methods and schemas for better readability, consistency, and compliance with RFC specifications.
This commit is contained in:
Felipe Cardoso
2025-11-26 00:14:26 +01:00
parent 0ea428b718
commit dc875c5c95
6 changed files with 284 additions and 159 deletions
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126
backend/app/services/oauth_provider_service.py
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@@ -126,16 +126,22 @@ def hash_token(token: str) -> str:
def verify_pkce(code_verifier: str, code_challenge: str, method: str) -> bool:
"""Verify PKCE code_verifier against stored code_challenge."""
if method == "S256":
# SHA-256 hash, then base64url encode
digest = hashlib.sha256(code_verifier.encode()).digest()
computed = base64.urlsafe_b64encode(digest).rstrip(b"=").decode()
return secrets.compare_digest(computed, code_challenge)
elif method == "plain":
# Direct comparison (not recommended, but supported)
return secrets.compare_digest(code_verifier, code_challenge)
return False
"""
Verify PKCE code_verifier against stored code_challenge.
SECURITY: Only S256 method is supported. The 'plain' method provides
no security benefit and is explicitly rejected per RFC 7636 Section 4.3.
"""
if method != "S256":
# SECURITY: Reject any method other than S256
# 'plain' method provides no security against code interception attacks
logger.warning(f"PKCE verification rejected for unsupported method: {method}")
return False
# SHA-256 hash, then base64url encode (RFC 7636 Section 4.2)
digest = hashlib.sha256(code_verifier.encode()).digest()
computed = base64.urlsafe_b64encode(digest).rstrip(b"=").decode()
return secrets.compare_digest(computed, code_challenge)
def parse_scope(scope: str) -> list[str]:
@@ -198,10 +204,21 @@ async def validate_client(
if not client.client_secret_hash:
raise InvalidClientError("Client not configured with secret")
# Verify secret using SHA256 hash (consistent with CRUD)
computed_hash = hashlib.sha256(client_secret.encode()).hexdigest()
if not secrets.compare_digest(computed_hash, client.client_secret_hash):
raise InvalidClientError("Invalid client secret")
# SECURITY: Verify secret using bcrypt (not SHA-256)
# Supports both bcrypt and legacy SHA-256 hashes for migration
from app.core.auth import verify_password
stored_hash = str(client.client_secret_hash)
if stored_hash.startswith("$2"):
# New bcrypt format
if not verify_password(client_secret, stored_hash):
raise InvalidClientError("Invalid client secret")
else:
# Legacy SHA-256 format
computed_hash = hashlib.sha256(client_secret.encode()).hexdigest()
if not secrets.compare_digest(computed_hash, stored_hash):
raise InvalidClientError("Invalid client secret")
return client
@@ -246,9 +263,7 @@ def validate_scopes(client: OAuthClient, requested_scopes: list[str]) -> list[st
# Warn if some scopes were filtered out
invalid = requested - allowed
if invalid:
logger.warning(
f"Client {client.client_id} requested invalid scopes: {invalid}"
)
logger.warning(f"Client {client.client_id} requested invalid scopes: {invalid}")
return list(valid)
@@ -382,17 +397,17 @@ async def exchange_authorization_code(
f"Authorization code reuse detected for client {existing_code.client_id}"
)
await revoke_tokens_for_user_client(
db, existing_code.user_id, existing_code.client_id
db, UUID(str(existing_code.user_id)), str(existing_code.client_id)
)
raise InvalidGrantError("Authorization code has already been used")
else:
raise InvalidGrantError("Invalid authorization code")
# Now fetch the full auth code record
result = await db.execute(
auth_code_result = await db.execute(
select(OAuthAuthorizationCode).where(OAuthAuthorizationCode.id == updated_id)
)
auth_code = result.scalar_one()
auth_code = auth_code_result.scalar_one()
await db.commit()
if auth_code.is_expired:
@@ -413,10 +428,14 @@ async def exchange_authorization_code(
if client.client_type == "confidential":
if not client_secret:
raise InvalidClientError("Client secret required for confidential clients")
client = await validate_client(db, client_id, client_secret, require_secret=True)
client = await validate_client(
db, client_id, client_secret, require_secret=True
)
elif client_secret:
# Public client provided secret - validate it if given
client = await validate_client(db, client_id, client_secret, require_secret=True)
client = await validate_client(
db, client_id, client_secret, require_secret=True
)
# Verify PKCE
if auth_code.code_challenge:
@@ -424,8 +443,8 @@ async def exchange_authorization_code(
raise InvalidGrantError("code_verifier required")
if not verify_pkce(
code_verifier,
auth_code.code_challenge,
auth_code.code_challenge_method or "S256",
str(auth_code.code_challenge),
str(auth_code.code_challenge_method or "S256"),
):
raise InvalidGrantError("Invalid code_verifier")
elif client.client_type == "public":
@@ -443,8 +462,8 @@ async def exchange_authorization_code(
db=db,
client=client,
user=user,
scope=auth_code.scope,
nonce=auth_code.nonce,
scope=str(auth_code.scope),
nonce=str(auth_code.nonce) if auth_code.nonce else None,
device_info=device_info,
ip_address=ip_address,
)
@@ -487,16 +506,20 @@ async def create_tokens(
access_expires = now + timedelta(seconds=access_token_lifetime)
# Refresh token expiry
refresh_token_lifetime = int(client.refresh_token_lifetime or str(REFRESH_TOKEN_EXPIRY_DAYS * 86400))
refresh_token_lifetime = int(
client.refresh_token_lifetime or str(REFRESH_TOKEN_EXPIRY_DAYS * 86400)
)
refresh_expires = now + timedelta(seconds=refresh_token_lifetime)
# Create JWT access token
# SECURITY: Include all standard JWT claims per RFC 7519
access_token_payload = {
"iss": settings.OAUTH_ISSUER,
"sub": str(user.id),
"aud": client.client_id,
"exp": int(access_expires.timestamp()),
"iat": int(now.timestamp()),
"nbf": int(now.timestamp()), # Not Before - token is valid immediately
"jti": jti,
"scope": scope,
"client_id": client.client_id,
@@ -581,7 +604,7 @@ async def refresh_tokens(
OAuthProviderRefreshToken.token_hash == token_hash
)
)
token_record = result.scalar_one_or_none()
token_record: OAuthProviderRefreshToken | None = result.scalar_one_or_none()
if not token_record:
raise InvalidGrantError("Invalid refresh token")
@@ -608,36 +631,37 @@ async def refresh_tokens(
)
# Get user
user_result = await db.execute(
select(User).where(User.id == token_record.user_id)
)
user_result = await db.execute(select(User).where(User.id == token_record.user_id))
user = user_result.scalar_one_or_none()
if not user or not user.is_active:
raise InvalidGrantError("User not found or inactive")
# Validate scope (can only reduce, not expand)
original_scopes = set(parse_scope(token_record.scope))
token_scope = str(token_record.scope) if token_record.scope else ""
original_scopes = set(parse_scope(token_scope))
if scope:
requested_scopes = set(parse_scope(scope))
if not requested_scopes.issubset(original_scopes):
raise InvalidScopeError("Cannot expand scope on refresh")
final_scope = join_scope(list(requested_scopes))
else:
final_scope = token_record.scope
final_scope = token_scope
# Revoke old refresh token (token rotation)
token_record.revoked = True
token_record.last_used_at = datetime.now(UTC)
token_record.revoked = True # type: ignore[assignment]
token_record.last_used_at = datetime.now(UTC) # type: ignore[assignment]
await db.commit()
# Issue new tokens
device = str(token_record.device_info) if token_record.device_info else None
ip_addr = str(token_record.ip_address) if token_record.ip_address else None
return await create_tokens(
db=db,
client=client,
user=user,
scope=final_scope,
device_info=device_info or token_record.device_info,
ip_address=ip_address or token_record.ip_address,
device_info=device_info or device,
ip_address=ip_address or ip_addr,
)
@@ -685,7 +709,7 @@ async def revoke_token(
if client_id and refresh_record.client_id != client_id:
raise InvalidClientError("Token was not issued to this client")
refresh_record.revoked = True
refresh_record.revoked = True # type: ignore[assignment]
await db.commit()
logger.info(f"Revoked refresh token {refresh_record.jti[:8]}...")
return True
@@ -699,7 +723,10 @@ async def revoke_token(
token,
settings.SECRET_KEY,
algorithms=[settings.ALGORITHM],
options={"verify_exp": False, "verify_aud": False}, # Allow expired tokens
options={
"verify_exp": False,
"verify_aud": False,
}, # Allow expired tokens
)
jti = payload.get("jti")
if jti:
@@ -713,7 +740,7 @@ async def revoke_token(
if refresh_record:
if client_id and refresh_record.client_id != client_id:
raise InvalidClientError("Token was not issued to this client")
refresh_record.revoked = True
refresh_record.revoked = True # type: ignore[assignment]
await db.commit()
logger.info(
f"Revoked refresh token via access token JTI {jti[:8]}..."
@@ -756,7 +783,7 @@ async def revoke_tokens_for_user_client(
count = 0
for token in tokens:
token.revoked = True
token.revoked = True # type: ignore[assignment]
count += 1
if count > 0:
@@ -793,7 +820,7 @@ async def revoke_all_user_tokens(db: AsyncSession, user_id: UUID) -> int:
count = 0
for token in tokens:
token.revoked = True
token.revoked = True # type: ignore[assignment]
count += 1
if count > 0:
@@ -843,7 +870,9 @@ async def introspect_token(
token,
settings.SECRET_KEY,
algorithms=[settings.ALGORITHM],
options={"verify_aud": False}, # Don't require audience match for introspection
options={
"verify_aud": False
}, # Don't require audience match for introspection
)
# Check if associated refresh token is revoked
@@ -953,9 +982,10 @@ async def grant_consent(
if consent:
# Merge scopes
existing = set(parse_scope(consent.granted_scopes))
granted = str(consent.granted_scopes) if consent.granted_scopes else ""
existing = set(parse_scope(granted))
new_scopes = existing | set(scopes)
consent.granted_scopes = join_scope(list(new_scopes))
consent.granted_scopes = join_scope(list(new_scopes)) # type: ignore[assignment]
else:
consent = OAuthConsent(
user_id=user_id,
@@ -993,7 +1023,7 @@ async def revoke_consent(
await revoke_tokens_for_user_client(db, user_id, client_id)
await db.commit()
return result.rowcount > 0
return result.rowcount > 0 # type: ignore[attr-defined]
# ============================================================================
@@ -1016,7 +1046,7 @@ async def cleanup_expired_codes(db: AsyncSession) -> int:
)
)
await db.commit()
return result.rowcount
return result.rowcount # type: ignore[attr-defined]
async def cleanup_expired_tokens(db: AsyncSession) -> int:
@@ -1036,4 +1066,4 @@ async def cleanup_expired_tokens(db: AsyncSession) -> int:
)
)
await db.commit()
return result.rowcount
return result.rowcount # type: ignore[attr-defined]