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A signup system has three separate jobs: create a unique account identity, verify only what the account actually needs to prove, and store optional profile data and user-to-user relationships in tables that reflect what those data mean. There is no single correct signup flow or schema. The right choices depend on what the account protects, who may register, and what a relationship between two users is supposed to represent.
Start with what the account has to prove
Most signup problems begin with mixing up three different questions. Authentication asks whether the person presenting an account controls it. Identity proofing asks whether the account is bound to a real person. Authorization asks whether that authenticated account may perform a specific action on a specific record. A user record in your database establishes a unique identity inside your service, but it does not have to identify a real-world person.
Authentication, proofing, and authorization are different controls
- Authentication verifies a claimed identity using one or more authenticators, such as a password, a one-time code, or a passkey. OWASP defines it as verifying an individual, entity, or website based on authenticators.
- Identity proofing is a separate step that binds an account to a real person, usually by checking documents or other evidence. Many consumer services never need it.
- Authorization is checked on every request. Being logged in does not mean a user may read or change every profile or relationship record.
Decide the registration rules before writing the form
OWASP’s registration guidance says identity requirements should follow from business and security requirements. Answer these questions before you design the signup screens:
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- Does a person or an automated rule vet each account, or are accounts created immediately?
- May one person register more than once, and how are duplicates detected?
- Can a user choose a role at signup, or is the role assigned by an administrator?
- What proof of identity is required, and at what point in the lifecycle?
- Is the registered identity verified at all, and what happens if verification never completes?
Treat the registration path as untrusted input. Every field a user submits, including role, tenant, or account type, should be validated on the server and never accepted just because the form offered it.
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For a low-risk community profile, confirming control of an email address may be enough. For regulated or high-impact access, the application may need stronger proofing. NIST’s SP 800-63-4 guidelines describe identity proofing, enrollment, authenticators, federation, and related assertions, and its companion SP 800-63A-4, published in final form on July 31, 2025, defines three identity assurance levels for proofing and enrollment. NIST states that the guidelines cover users who “interact with government information systems over networks.” They are written for federal systems, so treat them as a structured vocabulary for assurance levels rather than a rulebook for every consumer signup. Your own legal and regulatory obligations determine which level, if any, you need.
Designing the signup and verification flow
OWASP allows an email address to serve as the username when the address has been verified during signup, but it also recommends letting users choose a username that is not an email address. Verifying an email proves control of that mailbox. It does not prove that the person is who they claim to be.
A practical email verification sequence
- Accept the email address and normalize it (trim whitespace and lowercase the domain part) before checking for an existing account.
- Create the account in a pending state, with no privileged capabilities, and generate a single-use verification token with a short expiry.
- Send the token by email. Store only a hash of the token, so a database leak does not expose working links.
- When the link is opened, check the token, mark the email as verified, and activate the account in one transaction so a token cannot be reused.
- Require a fresh authentication event before changing the email address or other recovery settings later.
Do not reveal whether an account exists
Signup, login, and password recovery responses should not say whether a username or email is already registered. OWASP’s digital identity developer guidance recommends generic failure messages and avoiding response differences in timing that would reveal account existence. A common pattern is to send “check your inbox to continue” for both new and existing addresses, and to send an email to the owner of an existing account instead of showing an error on screen.
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Keep account identity and optional profile attributes conceptually distinct when the product needs that separation. The account holds identity and state: the internal identifier, credentials references, verification status, and whether the account is active. The profile holds user-facing attributes such as a display name, biography, avatar, or location. A profile may not exist yet, and some users may never create one.
A one-to-one relation can be modeled either way. In the separate-table approach, the profile row carries a foreign key to the user, and that key is also unique (or is the primary key), so at most one profile can point to a given user. A user can exist without a profile, and a profile cannot point to a user that does not exist. Prisma’s documentation uses this same logic in its one-to-one example: the profile requires a user, while the user does not require a profile. Microsoft’s database design overview also notes that a one-to-one relationship can sometimes be combined into a single table, so splitting is a design choice, not a rule.
| Factor | Same table (user and profile columns together) | Separate profile table |
|---|---|---|
| Profile optional for most users | Many nullable columns that are empty until a profile is created | Profile row exists only when created; account can stand alone |
| Access boundaries | Public and private columns sit beside security-sensitive fields, so queries must be careful about what they select | Profile can be read through its own query path and access rules, separate from credentials and account state |
| Expected attributes | Fine when the set is small and stable | Better when attributes grow, vary by user type, or need their own history |
| Query patterns | One lookup returns everything, with fewer joins | Requires a join or second query when account and profile are needed together |
A minimal separate-table schema, written in PostgreSQL-style SQL, looks like this:
CREATE TABLE users (
id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
email TEXT NOT NULL UNIQUE,
email_verified_at TIMESTAMPTZ,
status TEXT NOT NULL DEFAULT 'pending'
);
CREATE TABLE profiles (
user_id BIGINT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
display_name TEXT NOT NULL,
bio TEXT,
updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
);Here the primary key on profiles.user_id enforces one profile per user, and the foreign key guarantees the profile refers to an existing account. The ON DELETE CASCADE clause is a deliberate choice; for some products, retaining profile history after account closure is the correct behavior instead.
Modeling relationships between users
Identify the entities and cardinality before choosing ORM syntax or table layouts. A relationship between users is an association with a meaning: follows, friendships, team membership, invitations, or blocks. Each of those meanings implies different rules.
Many-to-many links use a join table
When a user can have many connections and each connection involves many users, use an association table with a foreign key for each side. A composite primary key, or an equivalent uniqueness constraint, prevents the same pair from being stored twice. PostgreSQL’s documentation illustrates this pattern and explains that foreign keys restrict associations to rows that actually exist.
CREATE TABLE user_connections (
requester_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
addressee_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
status TEXT NOT NULL DEFAULT 'requested',
created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
PRIMARY KEY (requester_id, addressee_id),
CHECK (requester_id <> addressee_id)
);This design treats the link as directional, since requester_id and addressee_id have different meanings. If the relationship is symmetric, such as “friends,” you must decide how to store one row rather than two, for example by always writing the lower ID first. Whether both users must consent is a product rule that the schema can record but cannot decide for you.
Promote the link to an entity when it carries data
A plain join table is enough when the link is only a pair of IDs. Once the association has state or history, it becomes a first-class entity. Typical attributes include invitation status, acceptance time, who initiated the link, whether it was blocked, and where it came from. Keeping those fields on the relationship row, rather than on either user, keeps the data attached to the association it describes. This is a design judgment based on the fact that those attributes describe the link itself, not something the database forces on you.
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Define deletion and retention rules before you ship
- Cascade: deleting a user removes all their links. Simple, but it erases history the other party may still rely on.
- Restrict: the account cannot be deleted while links exist. Forces a cleanup step, which can frustrate users.
- Retain: the account is anonymized or deactivated and links remain, perhaps with a status such as
closed. Better for audit trails, but requires your privacy policy and deletion requests to address retained data.
Preventing access to other users’ profiles and relationships
Authorization must be checked on the server for every profile and relationship read or write. The most common failure is an insecure direct object reference: an endpoint accepts a user ID from the URL or body and returns or changes that record without checking whether the caller is allowed to access it. OWASP’s IDOR guidance describes exactly this risk.
A server-side check for each operation
- Take the acting user’s ID from the authenticated session or validated token, never from a request parameter.
- Load the requested object and compare its owner or permitted relations with the acting user.
- For relationship operations, check both parties: a user may accept a request addressed to them but may not accept one addressed to someone else.
- Return a generic “not found” response when the caller lacks access, so the response does not reveal that the record exists.
- Scope database queries by the acting user where possible, for example
WHERE id = $1 AND owner_id = $2, so a missing check fails safe.
Unguessable IDs help, but they are not the control
OWASP recommends randomly generated user identifiers rather than sequential ones, because sequential IDs are easy to enumerate and infer. Random identifiers reduce that exposure, but a user who knows another user’s ID must still be blocked by the permission check. Treat random IDs as defense in depth, not as access control.
Database credentials and operational safeguards
- Keep database credentials out of source control. Load them from a secrets manager or the deployment environment, and rotate them when staff or systems change.
- Give the application database account only the privileges it needs. OWASP recommends limiting privileges and restricting access to required hosts, databases, and operations, so the application role should not own tables or run schema changes.
- Run migrations with a separate, more privileged account used only during deployment.
- Log authentication and authorization failures, but do not log passwords, verification tokens, or full profile payloads.
Build or buy the authentication layer
Authentication ownership is the most consequential architecture decision in this area. An in-house system gives full control over flows and data, but you then own password storage, token handling, recovery, session management, and security updates. A managed identity service shifts much of that operational burden to a provider, at the cost of an external trust boundary, integration work, and dependence on the provider’s data handling terms. Whichever route you choose, your application still owns authorization for profiles and relationships. A managed login does not decide who may view a connection or edit a profile.
The evidence reviewed here does not establish that any particular provider is the right choice, so compare options against your own requirements for operational responsibility, integration effort, and data location.
The Bottom Line
Build signup around a unique account identity, verify email control at a level proportionate to the risk, keep optional profile data in a table that references the account with a unique key, and model relationships as join rows or first-class entities depending on whether they carry state. Above all, check every profile and relationship request against the authenticated user on the server.
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