Start login with any identity type

Start the login flow by providing any supported identifier:

• Email: user@example.com
• Phone: +15551234567 (E.164 format)
• Handle: @myhandle or myhandle
• Wallet: 0x1234... (EVM) or Solana address

Returns available authentication methods for the account.

For email/SMS: Use CDP SDK to authenticate, then call /auth/login/complete with the CDP token. For wallet: Sign the challenge message, then call /auth/login/complete with the signature.

Design notes (intentional disclosure):

• This endpoint returns wallet challenge messages (including full addresses). While this can reveal linked wallets for a handle, those wallets are already visible via public leaderboards. We accept this correlation risk as an explicit product decision.
• This endpoint also returns the available auth modalities (email/SMS/wallet) for a handle. This can reveal which channels are linked, but we accept this as an explicit product decision given public activity surfaces already imply these modalities.

Completion requirement: When calling /auth/login/complete, clients must send the exact identity_value for the chosen method (full email/phone/address) to disambiguate accounts with multiple identities of the same type.

The login session expires in 10 minutes.