azure-apim-unsupported-keyword

Azure APIM support

Authors:

• adamaltman Adam Altman (Redocly)

What this does and why

This catches OpenAPI usage unsupported or ignored by Azure API Management:

• operationId must be kebab-case and 76 characters max length.
• Operation summary must be 300 characters max length.
• Security is ignored.
• Only one server is used.
• $ref must be used for schemas and must only point to in-file components schemas (no external files or URLs).
• A table full of unsupported properties are flagged as errors.

Note that a lot of the usage contradicts best practices. As such, it might be more prudent to use a decorator to transform a richer OpenAPI description into one that is supported by Azure APIM as a step in a pipeline.

This ruleset can help validate the output of the decorator is viable for Azure APIM.

Azure APIM isn't prescriptive if unsupported features break the import/add/update process or if they are silently ignored. Users have a reported a combination of those behaviors.

Code

The first rule checks that the operationId conforms to the Azure APIM expectations of kebab-case and 76 max characters. It is set to be a warning level severity because Azure APIM automatically transforms non-compliant operationId values.

rules:
  rule/operation-pattern-azure-apim:
    subject: 
      type: Operation
      property: operationId
    assertions: 
      casing: kebab-case
      maxLength: 76
    severity: warn

The second rule checks that the operation summary is 300 characters max length.

  rule/summary-length-azure-apim:
    subject: 
      type: Operation
      property: summary
    assertions: 
      maxLength: 300
    severity: warn

The next rules highlights if there would be any servers that are ignored (and if you have any that don't use HTTPS):

  rule/multiple-servers-ignored-azure-apim:
    subject: 
      type: ServerList
    assertions: 
      maxLength: 1
    message: If multiple servers are specified, API Management will use the first HTTPS URL it finds.
    severity: warn
  
  rule/servers-not-https-azure-apim:
    subject: 
      type: Server
      property: url
    assertions: 
      pattern: '^https:\/\/.*'
    message: Server URL must start with HTTPS.

The next rule checks that schema is not defined inline (uses a $ref for MediaType schema). It also checks that the reference object link is to the components section of the same file which means it starts with #/components.

  rule/mediatype-schema-ref-pattern-azure-apim:
    subject: 
      type: MediaType
      property: schema
    message: Inline schema definitions and refs that point to URLs or files aren't supported.
    assertions:     
      ref: /^#\/components\/.*/

The next two rules ensure external docs and info summary aren't used.

  rule/external-docs-unsupported-azure-apim:
    subject: 
      type: ExternalDocs
    assertions: 
      defined: false
    message: Azure APIM does not support externalDocs.
  
  rule/info-summary-unsupported-azure-apim:
    subject: 
      type: Info
      property: summary
    assertions: 
      defined: false
    message: Azure APIM does not support Info summary.

APIM ignores security. This rule let's you know if it is left in there:

  rule/security-ignored-azure-apim:
    subject: 
      type: SecurityRequirementList
    assertions: 
      defined: false
    message: Azure APIM ignores security.

APIM documentation has a table of unsupported OpenAPI keywords. The following set of rules makes sure those features aren't used.

  rule/components-unsupported-azure-apim:
    subject: 
      type: Components
    assertions: 
      disallowed: 
        - responses
        - parameters
        - examples
        - requestBodies
        - headers
        - securitySchemes
        - links
        - callbacks
    message: Azure APIM does not support components other than schemas.
      
  rule/trace-unsupported-azure-apim:
    subject: 
      type: PathItem
    assertions: 
      disallowed: 
        - trace
    message: Azure APIM does not support trace operations.

  rule/path-item-servers-unsupported-azure-apim:
    subject: 
      type: PathItem
    assertions: 
      disallowed: 
        - servers
    message: Azure APIM does not support servers defined on path items.

  rule/operation-properties-unsupported-azure-apim:
    subject: 
      type: Operation
    assertions: 
      disallowed: 
        - externalDocs
        - callbacks
        - servers
        - security

  rule/parameter-properties-unsupported-azure-apim:
    subject: 
      type: Parameter
    assertions: 
      disallowed: 
        - allowEmptyValue
        - style
        - explode
        - allowReserved

Examples

The following snippets show how the configurable rules catch the likely bad uses of keywords.

Unsupported externalDocs

openapi: 3.1.0
externalDocs: https://example.com
# ...

Remove externalDocs to avoid any issues.

Allowed transformation

openapi: 3.1.0
# ...

The example OpenAPI description, a small cafe API, has a variety of unsupported features in use.

References

• https://learn.microsoft.com/en-us/azure/api-management/api-management-api-import-restrictions