Cedar Policy Language Support

This page describes how the application supports the Cedar policy language for defining and managing authorization rules.

What is Cedar?

Cedar is a policy language developed by AWS designed for fine-grained access control. It provides a declarative way to express authorization rules using principals (who), actions (what), and resources (on what).

The application uses Cedar as its underlying policy language, allowing you to:

• Define authorization rules using familiar concepts (subjects, actions, resources)
• Write conditions using Cedar expression syntax
• Export policies in Cedar format for use with compatible engines (e.g., Amazon Verified Permissions)
• Visualize your authorization schema as a Cedar schema diagram

Core Concepts

Mapping to Cedar

Application Concept	Cedar Concept	Description
Entity (User, Admin, etc.)	Principal Type	Who can perform actions
Entity (Document, Order, etc.)	Resource Type	What can be accessed
Entity Properties	Attributes	Data used in conditions
Actions (read, write, delete)	Actions	Operations that can be performed
Rules	Policies	Authorization decisions

Rule Structure

Every rule in the application maps to a Cedar policy with the following structure:

permit|forbid (
    principal is PrincipalType,
    action in [Action::"actionCode"],
    resource is ResourceType
)
when {
    // conditions that must be true
}
unless {
    // exceptions that block the rule
};

Writing Cedar Expressions

Expression Builder

The application provides an intelligent expression builder for writing when and unless conditions. The builder offers:

• Autocomplete suggestions based on your schema
• Syntax validation in real-time
• Color-coded highlighting for better readability

Available References

When writing expressions, you can reference:

Reference	Description	Example
subject	The principal requesting access	subject.department
resource	The resource being accessed	resource.owner
context	Runtime context information	context.ip
action	The action being performed	action

Operators

Comparison Operators:

• == - Equal to
• != - Not equal to
• <, >, <=, >= - Numeric comparisons
• in - Membership in a set
• like - Pattern matching (wildcards)
• has - Check if attribute exists

Logical Operators:

• && - Logical AND
• || - Logical OR
• ! - Logical NOT

Arithmetic Operators:

• + - Addition
• - - Subtraction
• * - Multiplication

Note: Cedar does not support division by design, to ensure policies remain analyzable and avoid division-by-zero issues.

Built-in Functions

Set Operations:

• contains(element) - Check if set contains element
• containsAll([elements]) - Check if set contains all elements
• containsAny([elements]) - Check if set contains any element

Date/Time Functions:

• duration("2h") - Create a duration value
• durationSince(datetime) - Time elapsed since a date
• toDate(value) - Convert to date
• toTime(value) - Convert to time
• toDateTime(value) - Convert to datetime

Expression Examples

Simple attribute comparison:

subject.department == "Finance"

Multiple conditions:

subject.role == "manager" && resource.status == "pending"

Set membership:

subject.clearanceLevel in ["secret", "top-secret"]

Set contains check:

subject.roles.contains("admin")

Pattern matching:

resource.name like "report-*"

Time-based condition:

context.requestTime.durationSince(resource.createdAt) < duration("24h")

Complex expression:

subject.role == "risk manager" && resource.amount > context.dailyLimit && context.newOverrideAmount <= context.standardLimit * 2

Cedar Schema

Viewing the Schema

Access the Cedar schema from the Entities page:

1. Navigate to Schema > Entities
2. Click the Cedar Schema button
3. The schema displays in JSON format

The schema viewer allows you to:

• View the complete Cedar schema definition
• Copy the schema to clipboard
• Download as a JSON file

Schema Structure

The Cedar schema defines:

{
  "Namespace": {
    "entityTypes": {
      "User": {
        "shape": {
          "type": "Record",
          "attributes": {
            "email": { "type": "String" },
            "department": { "type": "String" },
            "roles": { "type": "Set", "element": { "type": "String" } }
          }
        }
      }
    },
    "actions": {
      "read": {
        "appliesTo": {
          "principalTypes": ["User"],
          "resourceTypes": ["Document"]
        }
      }
    }
  }
}

Schema Diagram

The Cedar Schema Diagram provides a visual representation of your authorization model:

1. Navigate to Schema > Entities
2. Click the Cedar Schema button
3. Select the Diagram tab

The diagram shows:

• Principal entities (blue) - Who can perform actions
• Resource entities (orange) - What can be accessed
• Relationships - Arrows showing which actions connect principals to resources
• Attributes - Entity properties with their types

Cedar Policy Export

Viewing a Rule as Cedar Policy

Each rule can be exported as a Cedar policy:

1. Open a rule from the Rules list
2. Click the Cedar button in the toolbar
3. The policy displays in Cedar syntax

Policy Format

The exported policy follows the Cedar specification:

permit(
    principal is User,
    action in [Action::"approve"],
    resource is PurchaseOrder
)
when {
    subject.department == resource.department &&
    resource.amount <= subject.approvalLimit
}
unless {
    resource.status == "closed"
};

Using with Amazon Verified Permissions

The generated Cedar policies are compatible with Amazon Verified Permissions (AVP). To use your policies:

1. Export your Cedar schema
2. Export your rules as Cedar policies
3. Import both into your AVP policy store
4. Configure the AVP connector in your application

Expression Builder Features

Autocomplete

The expression builder provides intelligent autocomplete:

• After typing subject. - Shows available subject attributes
• After typing resource. - Shows available resource attributes
• After typing context. - Shows context attributes (ip, time, location, device, authenticated)
• After comparison operators - Suggests values and references
• After in - Suggests set syntax [...]
• After boolean expressions - Suggests logical operators (&&, ||)

Navigation

• Up/Down arrows - Navigate suggestions
• Enter or Tab - Select suggestion
• Escape - Close suggestions
• Type to filter - Suggestions filter as you type

Validation

Expressions are validated in real-time:

• Syntax errors appear below the input field
• Valid expressions show a success indicator
• Server-side validation confirms the expression can be parsed

Best Practices

Writing Effective Conditions

1. Keep conditions simple - Break complex rules into multiple simpler rules
2. Use meaningful attribute names - Makes policies self-documenting
3. Prefer explicit comparisons - Use == true instead of relying on truthiness
4. Test edge cases - Verify rules handle null/missing attributes

Organizing Your Schema

1. Define clear entity types - Separate principals from resources
2. Use consistent naming - Follow a naming convention for attributes
3. Set primary keys - Every entity should have a primary key defined
4. Document with descriptions - Add descriptions to entities and properties

Rule Design

1. Start with deny-by-default - Only permit what’s explicitly allowed
2. Use groups for role-based access - Simplifies rule management
3. Keep unless conditions focused - Use for specific exceptions only
4. Review generated Cedar policies - Verify they match your intent

Supported Cedar Features

Feature	Status	Notes
Permit/Forbid policies	Supported	Maps to rule effect
Principal constraints	Supported	Via subject entity type
Resource constraints	Supported	Via resource entity type
Action constraints	Supported	Via permissions/actions
When clauses	Supported	Expression builder
Unless clauses	Supported	Expression builder
Attribute access	Supported	Dot notation
Set operations	Supported	contains, containsAll, containsAny
Comparisons	Supported	All comparison operators
Logical operators	Supported	AND, OR, NOT
Pattern matching	Supported	like operator
Duration functions	Supported	duration, durationSince
If-then-else	Supported	Conditional expressions
Entity references	Supported	Via entity type properties

Troubleshooting

Common Expression Errors

“Unexpected token”

• Check for missing operators between expressions
• Verify string literals use double quotes

“Unknown attribute”

• Ensure the attribute exists on the entity
• Check spelling and case sensitivity

“Type mismatch”

• Verify you’re comparing compatible types
• Use appropriate functions for type conversion

Schema Issues

“No primary key defined”

• Add a primary key to the entity before using it in rules
• Primary keys are required for Cedar entity references

“Entity not available as reference”

• Ensure the target entity has a primary key
• Check that the entity type property is correctly configured