2fa is a two-factor authentication agent.
2fa -add [-7] [-8] [-hotp] name 2fa -list 2fa [-clip] name
“2fa -add name” adds a new key to the 2fa keychain with the given name. It prints a prompt to standard error and reads a two-factor key from standard input. Two-factor keys are short case-insensitive strings of letters A-Z and digits 2-7.
By default the new key generates time-based (TOTP) authentication codes; the -hotp flag makes the new key generate counter-based (HOTP) codes instead.
By default the new key generates 6-digit codes; the -7 and -8 flags select 7- and 8-digit codes instead.
“2fa -list” lists the names of all the keys in the keychain.
“2fa name” prints a two-factor authentication code from the key with the given name. If “-clip” is specified, 2fa also copies the code to the system clipboard.
With no arguments, 2fa prints two-factor authentication codes from all known time-based keys.
The default time-based authentication codes are derived from a hash of the key and the current time, so it is important that the system clock have at least one-minute accuracy.
The keychain is stored unencrypted in the text file $HOME/.2fa.
During GitHub 2FA setup, at the “Scan this barcode with your app” step, click the “enter this text code instead” link. A window pops up showing “your two-factor secret,” a short string of letters and digits.
Add it to 2fa under the name github, typing the secret at the prompt:
$ 2fa -add github 2fa key for github: nzxxiidbebvwk6jb $
Then whenever GitHub prompts for a 2FA code, run 2fa to obtain one:
$ 2fa github 268346 $
Or to type less:
$ 2fa 268346 github $