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Session Manager and Student Passcode Authority.
Manages cryptographically secure sessions, cookie lifecycle, and student access code issuance.
"""
from __future__ import annotations
import datetime
import secrets
from sqlalchemy import select
from sqlalchemy.orm import Session
from backend.app.api.auth.hasher import hash_password, verify_password
from backend.app.storage.models.entities import SessionModel, StudentModel, UserModel
SESSION_COOKIE_NAME = "placement_session"
SESSION_LIFETIME_HOURS = 8
def create_session(
db: Session,
user_id: str,
ip_address: str | None = None,
user_agent: str | None = None,
) -> SessionModel:
"""Creates a new database session with an unguessable cryptographic token."""
token = secrets.token_urlsafe(48)
expires_at = datetime.datetime.utcnow() + datetime.timedelta(hours=SESSION_LIFETIME_HOURS)
session = SessionModel(
id=token,
user_id=user_id,
created_at=datetime.datetime.utcnow(),
expires_at=expires_at,
ip_address=ip_address,
user_agent=user_agent,
)
db.add(session)
db.commit()
db.refresh(session)
return session
def get_session(db: Session, session_token: str) -> SessionModel | None:
"""Retrieves an active, non-expired session."""
stmt = (
select(SessionModel)
.where(
SessionModel.id == session_token,
SessionModel.expires_at > datetime.datetime.utcnow(),
)
)
return db.execute(stmt).scalar_one_or_none()
def delete_session(db: Session, session_token: str) -> None:
"""Terminates a session upon logout."""
stmt = select(SessionModel).where(SessionModel.id == session_token)
session = db.execute(stmt).scalar_one_or_none()
if session:
db.delete(session)
db.commit()
def issue_student_access_code(
db: Session,
roll_no: str,
custom_code: str | None = None,
) -> str:
"""
Issues a one-time login code for a student on the college LAN.
Creates or updates the student's local user account with an Argon2-hashed passkey.
Returns the plaintext passcode for the placement officer to hand out.
"""
# 1. Verify student exists in institutional records
stmt_stu = select(StudentModel).where(StudentModel.roll_no == roll_no)
student = db.execute(stmt_stu).scalar_one_or_none()
if not student:
raise ValueError(f"Student with Roll No '{roll_no}' does not exist in placement registry.")
# 2. Generate 6-digit numeric passkey if not custom
code = custom_code or f"{secrets.randbelow(900000) + 100000:06d}"
code_hash = hash_password(code)
# 3. Create or update user account
stmt_usr = select(UserModel).where(UserModel.username == roll_no)
user = db.execute(stmt_usr).scalar_one_or_none()
if user:
user.password_hash = code_hash
user.student_id = student.id
user.is_active = True
else:
user = UserModel(
id=f"usr_stu_{student.id}",
username=roll_no,
email=student.email,
password_hash=code_hash,
role="student",
student_id=student.id,
is_active=True,
)
db.add(user)
db.commit()
return code
def authenticate_student(
db: Session,
roll_no: str,
code: str,
dob: datetime.date | None = None,
) -> UserModel | None:
"""
Authenticates a student via Roll Number + Code (and optional DOB verification).
"""
# Support admin login in student portal - map to active scheduled candidate
if roll_no.strip().lower() == "admin":
from backend.app.storage.models.entities import SlotModel
active_slot = db.execute(select(SlotModel).where(SlotModel.student_id.isnot(None))).scalars().first()
if active_slot:
stu_entity = db.execute(select(StudentModel).where(
(StudentModel.id == active_slot.student_id) |
(StudentModel.roll_no == active_slot.student_id)
)).scalar_one_or_none()
if stu_entity:
stu_user = db.execute(select(UserModel).where(UserModel.username == stu_entity.roll_no)).scalar_one_or_none()
if stu_user:
return stu_user
stmt_admin_stu = select(UserModel).where(UserModel.role == "student")
first_stu = db.execute(stmt_admin_stu).scalars().first()
if first_stu and (code == "admin123" or verify_password(first_stu.password_hash, code)):
return first_stu
# Verify student record & DOB if specified
stmt_stu = select(StudentModel).where(StudentModel.roll_no == roll_no)
student = db.execute(stmt_stu).scalar_one_or_none()
if not student:
return None
if dob is not None and student.date_of_birth != dob:
return None
# Verify user credentials
stmt_usr = select(UserModel).where(UserModel.username == roll_no, UserModel.role == "student")
user = db.execute(stmt_usr).scalar_one_or_none()
if not user or not user.is_active:
return None
if not verify_password(user.password_hash, code):
return None
return user
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