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| 1 | +//! Personal access tokens — the credential a git client presents over HTTP Basic. |
| 2 | + |
| 3 | +use std::{fmt, time::SystemTime}; |
| 4 | + |
| 5 | +use sha2::{Digest, Sha256}; |
| 6 | +use subtle::ConstantTimeEq; |
| 7 | + |
| 8 | +use super::{DomainError, TokenId, UserId}; |
| 9 | + |
| 10 | +/// The prefix every Steid token carries. |
| 11 | +/// |
| 12 | +/// Present so a leaked token is recognisable as one — secret scanners key off exactly |
| 13 | +/// this — and so a value pasted into the wrong field is obviously a Steid credential. |
| 14 | +const TOKEN_PREFIX: &str = "steid_pat_"; |
| 15 | + |
| 16 | +/// How much of a token is kept in the clear to identify it afterwards. |
| 17 | +/// |
| 18 | +/// Enough for a person to tell two tokens apart in a list, far short of enough to |
| 19 | +/// guess the rest: the remaining 56 hex characters are still 224 bits. |
| 20 | +const DISPLAY_CHARS: usize = 8; |
| 21 | + |
| 22 | +/// A token in the clear. |
| 23 | +/// |
| 24 | +/// Exists for exactly as long as it takes to show it to whoever asked for it. Nothing |
| 25 | +/// stores this — the database holds only a [`TokenHash`] — so a token that is lost is |
| 26 | +/// gone, which is the property that makes the hash worth keeping. |
| 27 | +#[derive(Clone)] |
| 28 | +pub struct TokenSecret(String); |
| 29 | + |
| 30 | +impl TokenSecret { |
| 31 | + /// Bytes of entropy, matching [`SetupToken`](super::SetupToken). |
| 32 | + const BYTES: usize = 32; |
| 33 | + |
| 34 | + /// Mints a fresh token from the OS random source. |
| 35 | + pub fn generate() -> Self { |
| 36 | + use rand::Rng; |
| 37 | + |
| 38 | + let mut bytes = [0u8; Self::BYTES]; |
| 39 | + rand::rng().fill_bytes(&mut bytes); |
| 40 | + |
| 41 | + let random: String = bytes.iter().map(|byte| format!("{byte:02x}")).collect(); |
| 42 | + |
| 43 | + Self(format!("{TOKEN_PREFIX}{random}")) |
| 44 | + } |
| 45 | + |
| 46 | + /// Wraps a value presented by a client, which may be anything at all. |
| 47 | + pub fn from_presented(value: impl Into<String>) -> Self { |
| 48 | + Self(value.into()) |
| 49 | + } |
| 50 | + |
| 51 | + /// The token's hash, as stored. |
| 52 | + pub fn hash(&self) -> TokenHash { |
| 53 | + TokenHash::of(&self.0) |
| 54 | + } |
| 55 | + |
| 56 | + /// The leading characters kept in the clear, for naming the token in a list. |
| 57 | + /// |
| 58 | + /// Empty for a value that is not a Steid token at all, which only ever happens for |
| 59 | + /// something a client presented — and nothing displays those. |
| 60 | + pub fn display_prefix(&self) -> String { |
| 61 | + self.0 |
| 62 | + .strip_prefix(TOKEN_PREFIX) |
| 63 | + .unwrap_or_default() |
| 64 | + .chars() |
| 65 | + .take(DISPLAY_CHARS) |
| 66 | + .collect() |
| 67 | + } |
| 68 | + |
| 69 | + /// The token itself, to be shown exactly once. |
| 70 | + pub fn reveal(&self) -> &str { |
| 71 | + &self.0 |
| 72 | + } |
| 73 | +} |
| 74 | + |
| 75 | +/// Redacted, so a token cannot reach a log line except through [`reveal`](Self::reveal). |
| 76 | +impl fmt::Debug for TokenSecret { |
| 77 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 78 | + f.write_str("TokenSecret(redacted)") |
| 79 | + } |
| 80 | +} |
| 81 | + |
| 82 | +/// The SHA-256 of a token, hex-encoded. |
| 83 | +/// |
| 84 | +/// SHA-256 rather than Argon2 deliberately: a token is 256 bits from the OS random |
| 85 | +/// source, so there is no dictionary to slow an attacker down through, and this |
| 86 | +/// credential is verified on every request of every clone. See |
| 87 | +/// [0007](../../plans/decisions/0007-tokens-over-http-basic.md). |
| 88 | +#[derive(Clone, PartialEq, Eq, Hash)] |
| 89 | +pub struct TokenHash(String); |
| 90 | + |
| 91 | +impl TokenHash { |
| 92 | + /// Hashes a token. |
| 93 | + pub fn of(plaintext: &str) -> Self { |
| 94 | + let digest = Sha256::digest(plaintext.as_bytes()); |
| 95 | + |
| 96 | + Self(digest.iter().map(|byte| format!("{byte:02x}")).collect()) |
| 97 | + } |
| 98 | + |
| 99 | + /// Wraps an already-computed hash, typically one loaded from the database. |
| 100 | + pub fn from_trusted(value: impl Into<String>) -> Self { |
| 101 | + Self(value.into()) |
| 102 | + } |
| 103 | + |
| 104 | + pub fn as_str(&self) -> &str { |
| 105 | + &self.0 |
| 106 | + } |
| 107 | + |
| 108 | + /// Whether two hashes are the same, compared in constant time. |
| 109 | + /// |
| 110 | + /// Belt and braces: recovering a token from a timing signal on its *hash* would |
| 111 | + /// need a preimage attack. It costs nothing, and the day this is compared against |
| 112 | + /// something that is secret, the habit is already in place. |
| 113 | + pub fn matches(&self, other: &Self) -> bool { |
| 114 | + self.0.as_bytes().ct_eq(other.0.as_bytes()).into() |
| 115 | + } |
| 116 | +} |
| 117 | + |
| 118 | +/// Redacted for the same reason as [`TokenSecret`]: a hash in a log is a hash an |
| 119 | +/// attacker can compare against. |
| 120 | +impl fmt::Debug for TokenHash { |
| 121 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 122 | + f.write_str("TokenHash(redacted)") |
| 123 | + } |
| 124 | +} |
| 125 | + |
| 126 | +/// A personal access token, as recorded. |
| 127 | +/// |
| 128 | +/// Carries no scope. A token acts as the user who issued it, which is what |
| 129 | +/// personal-first means; narrowing that is a change to make when something actually |
| 130 | +/// needs it, behind an unchanged port. |
| 131 | +#[derive(Debug, Clone, PartialEq, Eq)] |
| 132 | +pub struct PersonalAccessToken { |
| 133 | + pub id: TokenId, |
| 134 | + pub user_id: UserId, |
| 135 | + /// What the person called it, so they can tell which one to revoke. |
| 136 | + pub name: String, |
| 137 | + /// The leading characters of the token, kept so a list can name one it cannot show. |
| 138 | + pub prefix: String, |
| 139 | + pub token_hash: TokenHash, |
| 140 | + pub created_at: SystemTime, |
| 141 | +} |
| 142 | + |
| 143 | +impl PersonalAccessToken { |
| 144 | + /// Longer than any label a person will type, short enough to bound a row. |
| 145 | + const MAX_NAME: usize = 100; |
| 146 | + |
| 147 | + /// Validates a new token record. |
| 148 | + pub fn new( |
| 149 | + id: TokenId, |
| 150 | + user_id: UserId, |
| 151 | + name: impl AsRef<str>, |
| 152 | + secret: &TokenSecret, |
| 153 | + created_at: SystemTime, |
| 154 | + ) -> Result<Self, DomainError> { |
| 155 | + let name = name.as_ref().trim(); |
| 156 | + |
| 157 | + if name.is_empty() { |
| 158 | + return Err(DomainError::validation( |
| 159 | + "name", |
| 160 | + "give the token a name so you can tell it apart later", |
| 161 | + )); |
| 162 | + } |
| 163 | + |
| 164 | + if name.chars().count() > Self::MAX_NAME { |
| 165 | + return Err(DomainError::validation( |
| 166 | + "name", |
| 167 | + format!("a token name is at most {} characters", Self::MAX_NAME), |
| 168 | + )); |
| 169 | + } |
| 170 | + |
| 171 | + Ok(Self { |
| 172 | + id, |
| 173 | + user_id, |
| 174 | + name: name.to_owned(), |
| 175 | + prefix: secret.display_prefix(), |
| 176 | + token_hash: secret.hash(), |
| 177 | + created_at, |
| 178 | + }) |
| 179 | + } |
| 180 | + |
| 181 | + /// Rebuilds a record from storage without revalidating it. |
| 182 | + pub fn from_trusted( |
| 183 | + id: TokenId, |
| 184 | + user_id: UserId, |
| 185 | + name: impl Into<String>, |
| 186 | + prefix: impl Into<String>, |
| 187 | + token_hash: TokenHash, |
| 188 | + created_at: SystemTime, |
| 189 | + ) -> Self { |
| 190 | + Self { |
| 191 | + id, |
| 192 | + user_id, |
| 193 | + name: name.into(), |
| 194 | + prefix: prefix.into(), |
| 195 | + token_hash, |
| 196 | + created_at, |
| 197 | + } |
| 198 | + } |
| 199 | +} |
| 200 | + |
| 201 | +#[cfg(test)] |
| 202 | +mod tests { |
| 203 | + use super::*; |
| 204 | + |
| 205 | + fn token(name: &str) -> Result<PersonalAccessToken, DomainError> { |
| 206 | + PersonalAccessToken::new( |
| 207 | + TokenId::generate(), |
| 208 | + UserId::generate(), |
| 209 | + name, |
| 210 | + &TokenSecret::generate(), |
| 211 | + SystemTime::UNIX_EPOCH, |
| 212 | + ) |
| 213 | + } |
| 214 | + |
| 215 | + #[test] |
| 216 | + fn a_generated_token_is_recognisable_and_full_width() { |
| 217 | + let secret = TokenSecret::generate(); |
| 218 | + |
| 219 | + assert!(secret.reveal().starts_with("steid_pat_")); |
| 220 | + assert_eq!( |
| 221 | + secret.reveal().len(), |
| 222 | + "steid_pat_".len() + TokenSecret::BYTES * 2 |
| 223 | + ); |
| 224 | + } |
| 225 | + |
| 226 | + #[test] |
| 227 | + fn tokens_are_unique_per_generation() { |
| 228 | + assert_ne!( |
| 229 | + TokenSecret::generate().reveal(), |
| 230 | + TokenSecret::generate().reveal() |
| 231 | + ); |
| 232 | + } |
| 233 | + |
| 234 | + #[test] |
| 235 | + fn a_token_hashes_to_the_same_value_every_time() { |
| 236 | + let secret = TokenSecret::generate(); |
| 237 | + |
| 238 | + assert!(secret.hash().matches(&secret.hash())); |
| 239 | + } |
| 240 | + |
| 241 | + #[test] |
| 242 | + fn different_tokens_hash_differently() { |
| 243 | + let first = TokenSecret::generate(); |
| 244 | + let second = TokenSecret::generate(); |
| 245 | + |
| 246 | + assert!(!first.hash().matches(&second.hash())); |
| 247 | + } |
| 248 | + |
| 249 | + #[test] |
| 250 | + fn a_presented_value_hashes_the_same_as_the_token_it_copies() { |
| 251 | + // This is the whole authentication path: what arrives over Basic is hashed and |
| 252 | + // compared against what was stored. |
| 253 | + let secret = TokenSecret::generate(); |
| 254 | + let presented = TokenSecret::from_presented(secret.reveal()); |
| 255 | + |
| 256 | + assert!(presented.hash().matches(&secret.hash())); |
| 257 | + } |
| 258 | + |
| 259 | + #[test] |
| 260 | + fn the_hash_is_not_the_token() { |
| 261 | + let secret = TokenSecret::generate(); |
| 262 | + |
| 263 | + assert_ne!(secret.hash().as_str(), secret.reveal()); |
| 264 | + assert_eq!(secret.hash().as_str().len(), 64); |
| 265 | + } |
| 266 | + |
| 267 | + #[test] |
| 268 | + fn the_display_prefix_identifies_without_revealing() { |
| 269 | + let secret = TokenSecret::generate(); |
| 270 | + let prefix = secret.display_prefix(); |
| 271 | + |
| 272 | + assert_eq!(prefix.len(), 8); |
| 273 | + assert!(secret.reveal().contains(&prefix)); |
| 274 | + assert!( |
| 275 | + !prefix.starts_with("steid_pat_"), |
| 276 | + "the prefix should identify the token, not the product" |
| 277 | + ); |
| 278 | + } |
| 279 | + |
| 280 | + #[test] |
| 281 | + fn a_value_that_is_not_a_steid_token_has_no_prefix() { |
| 282 | + assert_eq!(TokenSecret::from_presented("hunter2").display_prefix(), ""); |
| 283 | + } |
| 284 | + |
| 285 | + #[test] |
| 286 | + fn debug_output_redacts_both_the_token_and_its_hash() { |
| 287 | + let secret = TokenSecret::generate(); |
| 288 | + |
| 289 | + assert_eq!(format!("{secret:?}"), "TokenSecret(redacted)"); |
| 290 | + assert_eq!(format!("{:?}", secret.hash()), "TokenHash(redacted)"); |
| 291 | + assert!(!format!("{:?}", token("laptop").expect("valid")).contains(secret.reveal())); |
| 292 | + } |
| 293 | + |
| 294 | + #[test] |
| 295 | + fn a_token_records_its_prefix_and_hash() { |
| 296 | + let secret = TokenSecret::generate(); |
| 297 | + let record = PersonalAccessToken::new( |
| 298 | + TokenId::generate(), |
| 299 | + UserId::generate(), |
| 300 | + " laptop ", |
| 301 | + &secret, |
| 302 | + SystemTime::UNIX_EPOCH, |
| 303 | + ) |
| 304 | + .expect("valid"); |
| 305 | + |
| 306 | + assert_eq!(record.name, "laptop", "the name should be trimmed"); |
| 307 | + assert_eq!(record.prefix, secret.display_prefix()); |
| 308 | + assert!(record.token_hash.matches(&secret.hash())); |
| 309 | + } |
| 310 | + |
| 311 | + #[test] |
| 312 | + fn a_token_needs_a_name() { |
| 313 | + assert!(token("").is_err()); |
| 314 | + assert!(token(" ").is_err()); |
| 315 | + } |
| 316 | + |
| 317 | + #[test] |
| 318 | + fn a_name_has_a_limit() { |
| 319 | + assert!(token(&"a".repeat(PersonalAccessToken::MAX_NAME)).is_ok()); |
| 320 | + assert!(token(&"a".repeat(PersonalAccessToken::MAX_NAME + 1)).is_err()); |
| 321 | + } |
| 322 | +} |