> ## Documentation Index > Fetch the complete documentation index at: https://fal.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. # Sign file URL > Creates a signed URL that grants temporary access to a fal CDN file, regardless of its ACL. Useful for sharing access-restricted files. The signature is valid for `expiration_seconds` (up to 7 days). **Authentication:** Required. The API key must have the `assets:read` permission. ## OpenAPI ````yaml /api-reference/platform-apis/openapi/v1.json post /storage/files/sign openapi: 3.1.0 info: title: Platform APIs version: v1 description: fal REST API for programmatic access to platform resources. servers: - url: https://api.fal.ai/v1 description: Production server security: [] paths: /storage/files/sign: post: tags: - Storage summary: Sign file URL description: >- Creates a signed URL that grants temporary access to a fal CDN file, regardless of its ACL. Useful for sharing access-restricted files. The signature is valid for `expiration_seconds` (up to 7 days). **Authentication:** Required. The API key must have the `assets:read` permission. operationId: signStorageFileUrl parameters: - schema: type: string format: uri description: >- Full URL of the fal CDN file, as returned by the upload APIs (https://v3.fal.media/files/b//). Must not contain query parameters. example: https://v3.fal.media/files/b/0a1b2c3d/output.png required: true description: >- Full URL of the fal CDN file, as returned by the upload APIs (https://v3.fal.media/files/b//). Must not contain query parameters. name: url in: query requestBody: required: true content: application/json: schema: type: object properties: expiration_seconds: type: integer minimum: 1 maximum: 604800 description: How long the signed URL stays valid, in seconds (max 7 days) example: 3600 required: - expiration_seconds additionalProperties: false description: Signing options for the file URL example: expiration_seconds: 3600 responses: '200': description: Signed URL granting temporary access content: application/json: schema: type: object properties: signed_url: type: string description: URL with an embedded signature granting temporary access example: >- https://v3.fal.media/files/b/0a1b2c3d/output.png?identity=... required: - signed_url description: Signed URL response example: signed_url: https://v3.fal.media/files/b/0a1b2c3d/output.png?identity=... '400': description: Invalid request parameters content: application/json: schema: type: object properties: error: type: object properties: type: type: string enum: - authorization_error - validation_error - not_found - rate_limited - server_error - not_implemented description: The category of error that occurred message: type: string description: Human-readable error message docs_url: type: string format: uri description: Link to relevant documentation request_id: type: string description: Unique request identifier for debugging required: - type - message description: Error details required: - error description: Standard error response format example: error: type: validation_error message: Invalid request parameters '401': description: Authentication required content: application/json: schema: type: object properties: error: type: object properties: type: type: string enum: - authorization_error - validation_error - not_found - rate_limited - server_error - not_implemented description: The category of error that occurred message: type: string description: Human-readable error message docs_url: type: string format: uri description: Link to relevant documentation request_id: type: string description: Unique request identifier for debugging required: - type - message description: Error details required: - error description: Standard error response format example: error: type: authorization_error message: Authentication required '403': description: Access denied content: application/json: schema: type: object properties: error: type: object properties: type: type: string enum: - authorization_error - validation_error - not_found - rate_limited - server_error - not_implemented description: The category of error that occurred message: type: string description: Human-readable error message docs_url: type: string format: uri description: Link to relevant documentation request_id: type: string description: Unique request identifier for debugging required: - type - message description: Error details required: - error description: Standard error response format example: error: type: authorization_error message: Access denied '404': description: Resource not found content: application/json: schema: type: object properties: error: type: object properties: type: type: string enum: - authorization_error - validation_error - not_found - rate_limited - server_error - not_implemented description: The category of error that occurred message: type: string description: Human-readable error message docs_url: type: string format: uri description: Link to relevant documentation request_id: type: string description: Unique request identifier for debugging required: - type - message description: Error details required: - error description: Standard error response format example: error: type: not_found message: Resource not found '429': description: Rate limit exceeded content: application/json: schema: type: object properties: error: type: object properties: type: type: string enum: - authorization_error - validation_error - not_found - rate_limited - server_error - not_implemented description: The category of error that occurred message: type: string description: Human-readable error message docs_url: type: string format: uri description: Link to relevant documentation request_id: type: string description: Unique request identifier for debugging required: - type - message description: Error details required: - error description: Standard error response format example: error: type: rate_limited message: Rate limit exceeded '500': description: Internal server error content: application/json: schema: type: object properties: error: type: object properties: type: type: string enum: - authorization_error - validation_error - not_found - rate_limited - server_error - not_implemented description: The category of error that occurred message: type: string description: Human-readable error message docs_url: type: string format: uri description: Link to relevant documentation request_id: type: string description: Unique request identifier for debugging required: - type - message description: Error details required: - error description: Standard error response format example: error: type: server_error message: An unexpected error occurred security: - apiKey: [] components: securitySchemes: apiKey: type: apiKey in: header name: Authorization description: >- API key must be prefixed with "Key ", e.g. Authorization: Key YOUR_API_KEY ````