Difficult Terrain and Provoke

[Reaves]

We are playing pathfinder and can't find the appropriate ruling.
If the area is considered difficult terrain, does it provoke someone if they move into a 5 foot square next to an enemy or creature.
The argument is that the area is considered 10 foot movement. So moving into it will either provoke or not.
It is understood that leaving a threatened square will provoke.
Please help me answer this question.

[Gamesman02]

Unless you have certain feats, you cannot take a 5' step in difficult terrain. Any movement is considered a move action. So, does the move action in question provoke?

[Majuba]

Entering a threatened square, regardless of how much movement it takes to do so, does not provoke an attack of opportunity.

About the only exception to this is when you're using more than a 5' step to pass through the corners of a 10' reach.

[SlimGauge]

Remember, it is attempting to EXIT a threatened square that provokes, not entering one.

Rules wrote:

Moving: Moving out of a threatened square usually provokes attacks of opportunity from threatening opponents.

Bolding is mine.

[Cornielius]

Take 5-Foot Step (from the PRD)
You can move 5 feet in any round when you don't perform any other kind of movement. Taking this 5-foot step never provokes an attack of opportunity. You can't take more than one 5-foot step in a round, and you can't take a 5-foot step in the same round that you move any distance.

You can take a 5-foot step before, during, or after your other actions in the round.

You can only take a 5-foot-step if your movement isn't hampered by difficult terrain or darkness. Any creature with a speed of 5 feet or less can't take a 5-foot step, since moving even 5 feet requires a move action for such a slow creature.

You may not take a 5-foot step using a form of movement for which you do not have a listed speed.

So the 5 ft step option is not allowed. (Though there are several special abilities that give a character the ability to take the 5 ft step in certain terrains.)

Whether the square requires 10 ft of movement doesn't change the fact it is a single square.

So I would say that no, moving 1 square in difficult terrain to end up adjacent to an enemy does not provoke, but does count as a move action.
If the opponent has reach, factor it in normally, looking at squares, not the amount of movement necessary to cross the one square.

[Hendelbolaf]

If it is difficult terrain and you attempt to move out of a threatened square then you WILL provoke an attack of opportunity.

For example, if a caster is adjacent to a foe and they are in difficult terrain and the caster wants to move 5 feet away so that he can safely cast a spell without casting defensively, then the caster would provoke an attack of opportunity from the movement.

If a rogue wanted to position himself in a different adjacent square to him and the enemy, then that would provoke an attack of opportunity in difficult terrain.

The distance is still only 5 feet but the action required was more than a simple adjust so the action is what is provoking the attack of opportunity per the rules on both action types and attacks of opportunity in the Combat section of the CRB.