Programmatic policy creation using JSON policy format

You can use the Cedar Policy::to_json() method to convert the specified policy into a JSON document.

You can also use the Policy::from_json() method to convert a JSON document into a new Cedar policy. This gives you another option for programmatically constructing or parsing your policies.

The JSON document format you receive or submit using either of these methods is described in this topic.

Example

A “standard” Cedar policy looks like the following:

permit (
    principal == User::"12UA45",
    action == Action::"view",
    resource in Folder::"abc"
) when {
    context.tls_version == "1.3"
};

When you retrieve the JSON representation of this policy, it looks like the following:

{
    "effect": "permit",
    "principal": {
        "op": "==",
        "entity": { "type": "User", "id": "12UA45" }
    },
    "action": {
        "op": "==",
        "entity": { "type": "Action", "id": "view" }
    },
    "resource": {
        "op": "in",
        "entity": { "type": "Folder", "id": "abc" }
    },
    "conditions": [
        {
            "kind": "when",
            "body": {
                "==": {
                    "left": {
                        ".": {
                            "left": {
                                "Var": "context"
                            },
                            "attr": "tls_version"
                        }
                    },
                    "right": {
                        "Literal": "1.3"
                    }
                }
            }
        }
    ]
}

In this topic, the term policy refers to both static policies and policy templates.

The JSON representation of a Cedar policy does not preserve comments, whitespace, or newline characters.

The JSON representation of a policy contains the following keys:

effect
principal
action
resource
conditions
annotations

`effect`

The effect object is required.

The value of this object must be either the string permit or the string forbid.

"effect": "permit",
"effect": "forbid",

`principal`

The principal object is required.

The value of this object must include an object with the key op, and depending on the value of op, an object with the key entity or slot.

`op`

The op key is required. The op object must have one of the following string values:

All

If present, then the original policy contains only the key word principal with no constraints. In this case, the principal object doesn’t require any additional objects.

Example

Cedar policy line:
```
  principal
```
JSON representation:
```
  "principal": {
      "op": "All" 
  }
```

==
If present, then the principal object must also have one of the following:

entity

Example

Cedar policy line:

principal == User::"12UA45"

JSON representation:

"principal": {
    "op": "==",
    "entity": { "type": "User", "id": "12UA45" }
}

slot

Example

Cedar policy line:

principal == ?principal

JSON representation:

"principal": {
    "op": "==",
    "slot": { "?principal" }
},

in

If present, then the principal object must also have one of the following:

entity

Example

Cedar policy line:

principal in Group::"Admins"

JSON representation:

"principal": {
    "op": "in",
    "entity": { "type": "Group", "id": "Admins" }
}

slot

Example

Cedar policy line:

principal in ?principal

JSON representation

"principal": {
    "op": "in",
    "slot": { "?principal" }
},

is

If present, then the principal object must also have an entity_type key.

Example

Cedar policy line:

principal is User

JSON representation:

"principal": {
    "op": "is",
    "entity_type": "User"
}

The principal object may also optionally have an in key. The value of this key is an object with one of the following:

entity

Example

Cedar policy line:

principal is User in Group::"Admins"

JSON representation:

"principal": {
    "op": "is",
    "entity_type": "User",
    "in": {
        "entity": { "type": "Group", "id": "Admins" }
    }
}

slot

Example

Cedar policy line:

principal is User in ?principal

JSON representation

"principal": {
    "op": "is",
    "entity_type": "User",
    "in": {
        "slot": { "?principal" }
    }
},

`action`

The action object is required.

The value of this object must include an object with the key op, and depending on the value of op, an object with the key [entity](#entity) or [entities](#entities).

`op`

The op key is required.

The op object must have one of the following string values:

All

If present, then the original policy contains only the key word action with no constraints. In this case, the action object doesn’t require any additional objects.

Example

Cedar policy line:
```
  action
```
JSON representation:
```
  "action": {
      "op": "All" 
  }
```
==

If present, then the action object must also have the following object:
- entity
  
  Example
  
  Cedar policy line:
```
action == Action::"readFile"
```
  JSON representation:
```
"action": {
    "op": "==",
    "entity": { "type": "Action", "id": "readFile" }
}
```

in

If present, then the action object must also have one of the following:

entity

Example

Cedar policy line:

action in Action::"readOnly"

JSON representation:

"action": {
    "op": "in",
    "entity": { "type": "Action", "id": "readOnly" }
}

entities

Example

Cedar policy line:

action in [ Action::"readFile", Action::"writeFile", Action::"deleteFile"]

JSON representation

"action": {
    "op": "in",
    "entities": [
        { "type": "Action", "id": "readFile" },
        { "type": "Action", "id": "writeFile" },
        { "type": "Action", "id": "deleteFile" }
    ]
}

`resource`

The resource object is required.

The value of this object must include an object with the key op, and depending on the value of op, an object with the key entity or slot.

`op`

The op key is required.

The op object must have one of the following string values:

All

If present, then the original policy contains only the key word resource with no constraints. In this case, the resource object doesn’t require any additional objects.

Example

Cedar policy line:
```
  resource
```
JSON representation:
```
  "resource": {
      "op": "All" 
  }
```

==

If this operator is present, then the resource object must also have one of the following:

entity

Example

Cedar policy line:

resource == file::"vacationphoto.jpg"

JSON representation:

"resource": {
    "op": "==",
    "entity": { "type": "file", "id": "vacationphoto.jpg" }
}

slot

Example

Cedar policy line:

resource == ?resource

JSON representation:

"resource": {
    "op": "==",
    "slot": { "?resource" }
},

in

If present, then the resource object must also have one of the following:

entity

Example

Cedar policy line:

resource in folder::"Public"

JSON representation:

"resource": {
    "op": "in",
    "entity": { "type": "folder", "id": "Public" }
}

slot

Example

Cedar policy line:

resource in ?resource

JSON representation

"resource": {
    "op": "in",
    "slot": { "?resource" }
}

is

If present, then the resource object must also have an entity_type key.

Example

Cedar policy line:

resource is file

JSON representation:

"resource": {
    "op": "is",
    "entity_type": "file"
}

The resource object may also optionally have an in key. The value of this key is an object with one of the following:

entity

Example

Cedar policy line:

resource is file in folder::"Public"

JSON representation:

"resource": {
    "op": "is",
    "entity_type": "file",
    "in": {
        "entity": { "type": "Folder", "id": "Public" }
    }
}

slot

Example

Cedar policy line:

resource is file in ?resource

JSON representation

"resource": {
    "op": "is",
    "entity_type": "file",
    "in": {
        "slot": { "?resource" }
    }
},

conditions

The conditions object is required.

The value of this object is a JSON array of objects. Each object in the array must have exactly two keys: kind and body.

The kind key must be either the string when or the string unless.

The body key must be an JsonExpr object.

Example

Cedar policy lines

when { ... }

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            ...
        }
    }
]

`annotations`

Annotations, if present, must be a JSON object. The keys and values, which must all be strings, correspond to the Cedar annotation keys and values on the policy.

`entity`

This object has a value that specifies the Cedar type and unique id of a single entity.

"entity": { "type": "User", "id": "12UA45" }

`entities`

This object is a JSON array or list of objects. Each entry in the list is a each with a value that specifies the type and id of the entity.

"entities": [
    { "type": "User", "id": "12UA45" },
    { "type": "Group", "id": "67VB89" }
]

`slot`

This key is required only if the policy being rendered is a template that uses a placeholder and the principal or resource object uses the == or in operator.

"slot": "?principal"
"slot": "?resource"

JsonExpr objects

An JsonExpr object is an object with a single key that is any of the following.

Value
Var
Slot
Unknown
! or neg operators
Binary operators: ==, !=, in, <, <=, >, >=, &&, ||, +, -, *, contains, containsAll, containsAny
., has
like
if-then-else
Set
Record
Any other key

`Value`

The value of this key is a Cedar value in the same syntax as expected for entity attribute values in Cedar’s entity format. This can include entity reference literals, set literals, and record literals.

Example with numeric literals

Cedar policy line:

when { 1 == 2 };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "==": {
                "left": {
                    "Value": 1
                },
                "right": {
                    "Value": 2
                }
            }
        }
    }
]

Example with entity literals

Cedar policy line

when { User::"alice" == Namespace::Type::"SomePrincipal" };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "==": {
                "left": {
                    "Value": {
                        "__entity": {
                            "type": "User",
                            "id": "alice"
                        }
                    }
                },
                "right": {
                    "Value": {
                        "__entity": {
                            "type": "Namespace::Type",
                            "id": "SomePrincipal"
                        }
                    }
                }
            }
        }
    }
]

Example with set literals

Cedar policy line:

when { [1, 2, "something"] == [4, 5, "otherthing"] };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "==": {
                "left": {
                    "Set": [
                        { "Value": 1 },
                        { "Value": 2 },
                        { "Value": "something" },
                    ]
                },
                "right": {
                    "Set": [
                        { "Value": 4 },
                        { "Value": 5 },
                        { "Value": "otherthing" },
                    ]
                }
            }
        }
    }
]

Example with record literals

Cedar policy line:

when { {something: "spam", otherthing: false} == {} };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "==": {
                "left": {
                    "Record": {
                        "something": { "Value": "spam" },
                        "otherthing": { "Value": false },
                    }
                },
                "right": {
                    "Record": {}
                }
            }
        }
    }
]

`Var`

The value of this key is one of the strings principal, action, resource, or context.

Example

Cedar policy line:

when { principal == action && resource == context };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "&&": {
                "left": {
                    "==": {
                        "left": {
                            "Var": "principal"
                        },
                        "right": {
                            "Var": "action"
                        }
                    }
                },
                "right": {
                    "==": {
                        "left": {
                            "Var": "resource"
                        },
                        "right": {
                            "Var": "context"
                        }
                    }
                }
            }
        }
    }
]

`Slot`

The value of this key is one of the strings ?principal or ?resource. Currently, policies containing this are not valid Cedar

`Unknown`

The value of this key is an object with a single key name, whose value is the name of the unknown. This is used for partial-evaluation. In particular, these values may appear in the JSON rendering of residuals.

`!` or `neg` operators

The value of this key is an object with a single key argument, whose value is itself an JsonExpr object.

Example using . and !

Example Cedar policy line:

when { !context.something };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
        "!": {
            "arg": {
                ".": {
                    "left": {
                        "Var": "context"
                    },
                    "attr": "something"
                }
            }
        }
    }
]

Binary operators: `==`, `!=`, `in`, `<`, `<=`, `>`, `>=`, `&&`, `||`, `+`, `-`, `*`, `contains`, `containsAll`, `containsAny`

The value for any of these keys is an object with keys left and right, which are each themselves an JsonExpr object.

Example for contains

Cedar policy line

when { principal.owners.contains("something") };

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "contains": {
                "left": {
                    ".": {
                        "left": {
                            "Var": "principal"
                        },
                        "attr": "owners"
                    }
                },
                "right": {
                    "Value": "something"
                }
            }
        }
    }
]

`.`, `has`

The value of one of these keys is an object with keys left and attr. The left key is itself an JsonExpr object, while the attr key is a string.

Example for .

Cedar policy line

context.something

JSON representation

".": {
    "left": {
        "Var": "context"
    },
    "attr": "something"
}

`is`

The value of this key is an object with the keys left and entity_type. The left key is itself an JsonExpr object, while the entity_type key is a string. The value may optionally have an in key which is also a JsonExpr object.

Example for is

Cedar policy line

principal is User in Group::"friends"

JSON representation

"is": {
    "left": { "Var": "principal" },
    "entity_type": "User",
    "in": {"entity": { "type": "Folder", "id": "Public" }}
}

`like`

The value of this key is an object with keys left and pattern. The left key is itself an JsonExpr object, while the pattern key is any string.

`if-then-else`

The value of this key is an object with keys if, then, and else, each of which are themselves an JsonExpr object.

Example for if-then-else

Cedar policy line

when {
    if context.something
    then principal has "-78/%$!"
    else resource.email like "*@amazon.com"
};

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "if-then-else": {
                "if": {
                    ".": {
                        "left": {
                            "Var": "context"
                        },
                        "attr": "something"
                    }
                },
                "then": {
                    "has": {
                        "left": {
                            "Var": "principal"
                        },
                        "attr": "-78/%$!"
                    }
                },
                "else": {
                    "like": {
                        "left": {
                            ".": {
                                "left": {
                                    "Var": "resource"
                                },
                                "attr": "email"
                            }
                        },
                        "pattern": "*@amazon.com"
                    }
                }
            }
        }
    }
]

`Set`

The value of this key is a JSON array of values, each of which is itself an JsonExpr object.

Example

Cedar policy element

[1, 2, "something"]

JSON representation

{
    "Set": [
        { "Value": 1 },
        { "Value": 2 },
        { "Value": "something" },
    ]
}

`Record`

The value of this key is a JSON object whose keys are arbitrary strings and values are themselves JsonExpr objects.

Example for record

Cedar policy element {something: "spam", somethingelse: false}

JSON representation

{
    "Record": {
        "foo": { "Value": "spam" },
        "somethingelse": { "Value": false },
    }
}

Any other key

This key is treated as the name of an extension function or method. The value must be a JSON array of values, each of which is itself an JsonExpr object. Note that for method calls, the method receiver is the first argument. For example, for a.isInRange(b), the first argument is for a and the second argument is for b.

Example for decimal function

Cedar policy line

decimal("10.0")

JSON representation

{
    "decimal": [
        {
            "Value": "10.0"
        }
    ]
}

Example for ip function and isInRange method

Cedar policy line

when {
    context.source_ip.isInRange(ip("222.222.222.0/24"))
};

JSON representation

"conditions": [
    {
        "kind": "when",
        "body": {
            "isInRange": [
                {
                    ".": {
                        "left": {
                            "Var": "context"
                        },
                        "attr": "source_ip"
                    }
                },
                {
                    "ip": [
                        {
                            "Value": "222.222.222.0/24"
                        }
                    ]
                }
            ]
        }
    }
]

Programmatic policy creation using JSON policy format

effect

principal

op

action

op

resource

op

conditions

annotations

entity

entities

slot

JsonExpr objects

Value

Var

Slot

Unknown

! or neg operators

Binary operators: ==, !=, in, <, <=, >, >=, &&, ||, +, -, *, contains, containsAll, containsAny

., has

is

like

if-then-else

Set

Record

Any other key

`effect`

`principal`

`op`

`action`

`op`

`resource`

`op`

`annotations`

`entity`

`entities`

`slot`

`Value`

`Var`

`Slot`

`Unknown`

`!` or `neg` operators

Binary operators: `==`, `!=`, `in`, `<`, `<=`, `>`, `>=`, `&&`, `||`, `+`, `-`, `*`, `contains`, `containsAll`, `containsAny`

`.`, `has`

`is`

`like`

`if-then-else`

`Set`

`Record`