curl --request POST \
  --url https://api.privy.io/v1/users/{user_id}/custom_metadata \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --header 'privy-app-id: <privy-app-id>' \
  --data '{
  "custom_metadata": {
    "key": "value"
  }
}'

{
  "id": "did:privy:cm3np4u9j001rc8b73seqmqqk",
  "created_at": 1731974895,
  "linked_accounts": [
    {
      "address": "[email protected]",
      "type": "email",
      "first_verified_at": 1674788927,
      "latest_verified_at": 1674788927,
      "verified_at": 1674788927
    },
    {
      "type": "farcaster",
      "fid": 4423,
      "owner_address": "0xE6bFb4137F3A8C069F98cc775f324A84FE45FdFF",
      "username": "payton",
      "display_name": "payton ↑",
      "bio": "engineering at /privy. building pixelpool.xyz, the first Farcaster video client. nyc. 👨‍💻🍎🏳️‍🌈  nf.td/payton",
      "profile_picture": "https://supercast.mypinata.cloud/ipfs/QmNexfCxdnFzWdJqKVgrjd27UGLMexNaw5FXu1XKR3cQF7?filename=IMG_2799.png",
      "profile_picture_url": "https://supercast.mypinata.cloud/ipfs/QmNexfCxdnFzWdJqKVgrjd27UGLMexNaw5FXu1XKR3cQF7?filename=IMG_2799.png",
      "verified_at": 1740678402,
      "first_verified_at": 1740678402,
      "latest_verified_at": 1741194370
    },
    {
      "type": "passkey",
      "credential_id": "Il5vP-3Tm3hNmDVBmDlREgXzIOJnZEaiVnT-XMliXe-BufP9GL1-d3qhozk9IkZwQ_",
      "authenticator_name": "1Password",
      "created_with_browser": "Chrome",
      "created_with_os": "Mac OS",
      "created_with_device": "Macintosh",
      "enrolled_in_mfa": true,
      "verified_at": 1741194420,
      "first_verified_at": 1741194420,
      "latest_verified_at": 1741194420
    }
  ],
  "mfa_methods": [
    {
      "type": "passkey",
      "verified_at": 1741194420
    }
  ],
  "has_accepted_terms": true,
  "is_guest": false
}