credential-paster

1import { atom, read, update } from 'claude-code'
2import type { EngineInterface, Register } from 'claude-code'
3
4import type { CredentialPasterRequest } from '../types'
5
6// A hidden paste field inside Claude Code. The model asks for a secret with the
7// `request_secret` tool; the person pastes it into a masked field in a pane;
8// the value goes straight to the paste-secret script via stdin and never into
9// the transcript, the model's context or this plugin's state.
10
11const PANE = 'paste-secret'
12const TOOL = 'request_secret'
13const BULLET = '•'
14const ESCAPES = ['auto', 'none', 'json', 'yaml', 'toml', 'dotenv', 'shell', 'url']
15const KEY_RE = /^[A-Za-z_][A-Za-z0-9_.]*$/
16const INPUT_SURFACES = ['terminal', 'desktop', 'vscode']
17
18const request = atom({ plugin: 'credential-paster', key: 'request' } as const, null)
19const typed = atom({ plugin: 'credential-paster', key: 'typed' } as const, 0)
20const error = atom({ plugin: 'credential-paster', key: 'error' } as const, null)
21
22// The secret lives only in this module's memory until it is written.
23let secret = ''
24
25// The field shows bullets; each change is diffed against them so the real
26// characters accumulate in `secret` (one contiguous edit per change).
27const applyEdit = (shown: string) => {
28  if (!shown.includes(BULLET)) {
29    secret = shown
30    return
31  }
32  let lead = 0
33  while (lead < shown.length && shown[lead] === BULLET) lead++
34  let trail = 0
35  while (trail < shown.length - lead && shown[shown.length - 1 - trail] === BULLET) trail++
36  const inserted = shown.slice(lead, shown.length - trail)
37  const keepTrail = Math.min(trail, Math.max(0, secret.length - lead))
38  secret = secret.slice(0, lead) + inserted + secret.slice(secret.length - keepTrail)
39}
40
41const describe = (r: CredentialPasterRequest) =>
42  r.key ? `${r.key} in ${r.file}` : `secret for ${r.file}`
43
44const scriptPath = ($: EngineInterface) =>
45  `${$.plugin.root}/skills/credential-paster/scripts/paste-secret`
46
47const scriptArgs = (r: CredentialPasterRequest) =>
48  r.placeholder
49    ? ['--placeholder', r.placeholder, '--escape', r.escape ?? 'auto', r.file]
50    : [r.file, r.key ?? '']
51
52const reset = async ($: EngineInterface) => {
53  secret = ''
54  await update($, request, () => null)
55  await update($, typed, () => 0)
56  await update($, error, () => null)
57}
58
59const openPane = ($: EngineInterface) =>
60  $.ui.open({ id: PANE, title: 'Paste secret', focus: true, closeOnEscape: true, rows: 6 })
61
62const cancel = async ($: EngineInterface, notify: boolean) => {
63  const r = await read($, request)
64  await reset($)
65  if (r && notify) {
66    void $.prompt.submit({
67      text: `[credential-paster] The user cancelled entering ${describe(r)}. Nothing was written.`,
68    })
69  }
70}
71
72const save = async ($: EngineInterface) => {
73  const r = await read($, request)
74  if (!r) return
75  if (secret.trim() === '') {
76    await update($, error, () => 'Nothing pasted yet.')
77    return
78  }
79  const value = secret
80  secret = ''
81  await update($, typed, () => 0)
82  const ran = await $.process.run(['bash', scriptPath($), '--stdin', ...scriptArgs(r)], {
83    stdin: value,
84  })
85  if (ran.exitCode !== 0) {
86    await update($, error, () => (ran.stderr.trim() || 'paste-secret failed.') + ' Paste again.')
87    return
88  }
89  await reset($)
90  await $.ui.close({ id: PANE })
91  $.ui.toast(`Saved ${describe(r)}`)
92  void $.prompt.submit({
93    text: `[credential-paster] ${ran.stdout.trim()} The user supplied the secret; continue the task. Never read or print it.`,
94  })
95}
96
97const parseRequest = (input: Record<string, unknown>): CredentialPasterRequest | string => {
98  const str = (k: string) => (typeof input[k] === 'string' ? (input[k] as string) : undefined)
99  const file = str('file')
100  const key = str('key')
101  const placeholder = str('placeholder')
102  const escape = str('escape')
103  if (!file) return '`file` is required.'
104  if (!key === !placeholder) return 'Give exactly one of `key` (dotenv) or `placeholder`.'
105  if (key && !KEY_RE.test(key)) return `Invalid key name '${key}'.`
106  if (placeholder && placeholder.length < 4) return 'Placeholder must be at least 4 characters.'
107  if (escape && !ESCAPES.includes(escape)) return `Unknown escape '${escape}'.`
108  return { file, key, placeholder, escape }
109}
110
111const start = async ($: EngineInterface, r: CredentialPasterRequest): Promise<string | null> => {
112  const surfaces = await $.session.surfaces()
113  if (!surfaces.some(s => INPUT_SURFACES.includes(s))) {
114    return 'No interactive Claude Code UI is attached. Use the paste-secret script from the credential-paster skill instead.'
115  }
116  if (r.placeholder) {
117    const check = await $.process.run(['bash', scriptPath($), '--check', ...scriptArgs(r)])
118    if (!check.stdout.startsWith('PENDING')) {
119      return `Placeholder not found: ${check.stdout.trim()} Write the placeholder into the file first.`
120    }
121  }
122  secret = ''
123  await update($, request, () => r)
124  await update($, typed, () => 0)
125  await update($, error, () => null)
126  await openPane($)
127  return null
128}
129
130// Tool and command are declared at session start. A plugin installed or
131// reloaded into a running session gets no session.start, so the next prompt
132// declares them instead. Module variables reset on reload, so this re-runs.
133let isRegistered = false
134
135const ensureRegistered = async ($: EngineInterface) => {
136  if (isRegistered) return
137  try {
138    await $.tool.register({
139      name: TOOL,
140      description:
141        'Ask the user for a secret (API key, token, password) through a masked paste field in the Claude Code UI and write it into a file. You never see the value. ' +
142        'Dotenv mode: give `file` and `key` (sets KEY=value, creates the file). ' +
143        'Any other format: first write a unique placeholder such as __PASTE_SECRET_TOKEN__ into the file, then give `file`, `placeholder` and `escape` ' +
144        '(json for JSON/YAML/TOML double-quoted strings, url for URLs, shell, dotenv, none; default auto by file extension). ' +
145        'Returns immediately: then END YOUR TURN and tell the user to paste the secret into the field. A message arrives once it is saved or cancelled.',
146      inputSchema: {
147        type: 'object',
148        properties: {
149          file: { type: 'string', description: 'Target file, relative to the working directory or absolute.' },
150          key: { type: 'string', description: 'Dotenv mode: variable name, e.g. OPENAI_API_KEY.' },
151          placeholder: { type: 'string', description: 'Placeholder mode: marker already present in the file.' },
152          escape: { type: 'string', enum: ESCAPES, description: 'Placeholder mode: how to escape the value.' },
153        },
154        required: ['file'],
155      },
156    })
157    await $.command.register({
158      name: 'paste-secret',
159      description: 'Paste a secret into a file through a hidden field (reopens a pending request)',
160      argumentHint: '[<file> <KEY>]',
161      immediate: true,
162    })
163    isRegistered = true
164  } catch {
165    // Session not bound yet: try again at the next event.
166  }
167}
168
169export const register: Register = on => {
170  on('session.start', async ($, e, next) => {
171    await ensureRegistered($)
172    return next(e)
173  })
174
175  on('prompt.submit', async ($, e, next) => {
176    await ensureRegistered($)
177    return next(e)
178  })
179
180  on('tool.call', { tool: 'mcp__credential-paster__request_secret' }, async ($, e) => {
181    const r = parseRequest(e as unknown as Record<string, unknown>)
182    if (typeof r === 'string') return { deny: r }
183    const failed = await start($, r)
184    if (failed) return { deny: failed }
185    return {
186      result:
187        `A masked paste field for ${describe(r)} is open in the user's Claude Code UI. ` +
188        'End your turn now and ask the user to paste the secret there and press Enter (they can type /paste-secret to reopen the field). ' +
189        'You will get a message when it is saved.',
190    }
191  })
192
193  on('command.run', { command: 'paste-secret' }, async ($, e) => {
194    const [file, key] = e.args.trim().split(/\s+/).filter(Boolean)
195    if (file) {
196      const r = parseRequest({ file, key })
197      if (typeof r === 'string') return { text: `paste-secret: ${r} Usage: /paste-secret <file> <KEY>` }
198      const failed = await start($, r)
199      return { text: failed ?? `Paste field open for ${describe(r)}.` }
200    }
201    const r = await read($, request)
202    if (!r) return { text: 'No secret requested. Usage: /paste-secret <file> <KEY>' }
203    await openPane($)
204    return { text: `Paste field open for ${describe(r)}.` }
205  })
206
207  on('ui.close', { id: PANE }, async ($, e, next) => {
208    // Escape or the close mark: treat as cancel. Our own close after saving
209    // finds no request left and stays quiet.
210    if (e.origin.kind === 'person') await cancel($, true)
211    return next(e)
212  })
213
214  on('ui.render', { component: 'Pane', requestId: PANE }, async ($, e) => {
215    if (e.surface === 'mobile') {
216      const { Text } = $.ui.resolve(e)
217      return <Text>Paste the secret on your computer: the mobile app has no input field.</Text>
218    }
219    const { Box, Text, Input, Button } = $.ui.resolve(e)
220    const r = await read($, request)
221    const count = await read($, typed)
222    const problem = await read($, error)
223
224    if (!r) {
225      return <Text dimColor>No secret requested.</Text>
226    }
227
228    return (
229      <Box flexDirection="column">
230        <Text>
231          Paste <Text bold>{describe(r)}</Text>
232          <Text dimColor> · hidden from Claude, written directly to the file</Text>
233        </Text>
234        <Input
235          key="secret"
236          label="Secret"
237          placeholder="paste here, then Enter"
238          value={BULLET.repeat(count)}
239          submitLabel="save"
240          autoFocus
241          onInput={value => {
242            applyEdit(value)
243            void update($, typed, () => secret.length)
244            void update($, error, () => null)
245          }}
246          onSubmit={value => {
247            applyEdit(value)
248            void save($)
249          }}
250        />
251        <Box>
252          <Button key="save" label="Save" variant="primary" onPress={() => void save($)} />
253          <Text> </Text>
254          <Button key="cancel" label="Cancel" role="dismiss" onPress={async () => { await cancel($, true); await $.ui.close({ id: PANE }) }} />
255        </Box>
256        {problem && <Text color="red">{problem}</Text>}
257      </Box>
258    )
259  })
260}
261

1export type CredentialPasterRequest = {
2  file: string
3  key?: string
4  placeholder?: string
5  escape?: string
6}
7
8declare module 'claude-code' {
9  interface PluginState {
10    'credential-paster': {
11      request: CredentialPasterRequest | null
12      typed: number
13      error: string | null
14    }
15  }
16}
17