Allow `derivedKeyAlgorithm == 'HKDF'` for `deriveKey()`

I would like to use deriveKey with PBKDF2 to derive a primary key from a primary password. I would then like to use HKDF to derive multiple independent operational keys (using different info parameters) from this primary key.

This feels like a fairly basic setup. However, I cannot find a "proper" way to realize it after perusing the WebCrypto documentation on MDN.

Here are two possible approaches I want to avoid:

• Derive the operational keys from the primary password, possibly using different salts
  This is highly inefficient, and not an acceptable solution. PBKDF2 is, by design, costly. Needing to run PBKDF2 ten times as often will require me to reduce the iteration count by the same factor to remain within responsiveness targets.
• Derive some number of bits from the primary password, then use importKey (with algorithm == 'HKDF')
  This is a feasible workaround. However, the point of deriveKey seems exactly to avoid needing to juggle raw key data in memory.

To me, the easiest medium-term solution to this issue would be to permit 'HKDF' as a value for deriveKey's derivedKeyAlgorithm - or potentially some object that specifies the number of bits required, where necessary?

The issue names no repository files or tests. Start with the linked MDN deriveKey documentation and the WebCrypto deriveKey specification entry, then determine how HKDF should be represented as derivedKeyAlgorithm and how required key length is specified. Done means the standards behavior is agreed and documented with suitable conformance coverage.