84 lines
2.5 KiB
Go
84 lines
2.5 KiB
Go
// Package auth provides JWT issuance + verification for the BFF.
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//
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// Tokens carry these claims:
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//
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// sub user id (UUID string)
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// tv token_version snapshot — middleware rejects if it doesn't match the
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// current value on the user row. Bumping the user's token_version
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// invalidates every JWT ever issued to that user (used on password
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// change and forced logout).
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// iat issued-at
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// exp expiry
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package auth
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import (
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"errors"
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"fmt"
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"time"
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"github.com/golang-jwt/jwt/v5"
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)
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// Claims is the JWT payload we sign + verify.
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type Claims struct {
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UserID string `json:"sub"`
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TokenVersion int `json:"tv"`
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jwt.RegisteredClaims
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}
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// Issuer issues and verifies tokens with a single shared HMAC secret.
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type Issuer struct {
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secret []byte
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ttl time.Duration
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}
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// NewIssuer returns an Issuer configured with the given HMAC secret and TTL.
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// The TTL is applied to every token issued via Issue().
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func NewIssuer(secret string, ttl time.Duration) *Issuer {
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return &Issuer{secret: []byte(secret), ttl: ttl}
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}
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// Issue mints a signed JWT for the given user.
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func (i *Issuer) Issue(userID string, tokenVersion int) (string, time.Time, error) {
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exp := time.Now().Add(i.ttl)
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claims := &Claims{
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UserID: userID,
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TokenVersion: tokenVersion,
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RegisteredClaims: jwt.RegisteredClaims{
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IssuedAt: jwt.NewNumericDate(time.Now()),
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ExpiresAt: jwt.NewNumericDate(exp),
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},
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}
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tok := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
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signed, err := tok.SignedString(i.secret)
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if err != nil {
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return "", time.Time{}, fmt.Errorf("sign jwt: %w", err)
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}
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return signed, exp, nil
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}
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// ErrInvalidToken is returned by Parse for any verification failure.
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var ErrInvalidToken = errors.New("invalid or expired token")
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// Parse validates the token's signature + expiry and returns the claims.
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// Callers must additionally compare claims.TokenVersion against the user's
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// current token_version (the JWT alone can't tell us whether the user has
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// since bumped their version).
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func (i *Issuer) Parse(raw string) (*Claims, error) {
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claims := &Claims{}
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tok, err := jwt.ParseWithClaims(raw, claims, func(t *jwt.Token) (any, error) {
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if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
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return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
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}
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return i.secret, nil
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})
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if err != nil || !tok.Valid {
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return nil, ErrInvalidToken
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}
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return claims, nil
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}
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// TTL returns the configured token lifetime. Handlers use it to set cookie
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// Max-Age so the cookie and the JWT expire in lockstep.
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func (i *Issuer) TTL() time.Duration { return i.ttl }
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